UW Physics

The relationship between the length of a spring and the force required to stretch the spring is shown below. What is the work done when the spring length is increased from 20 cm to 30 cm? A.25 J B.35 J C.250 J D.350 J

25 J

What is the ratio of the shortest to farthest distances between Earth and Mars as these planets orbit the Sun? On average, Earth is 150 million km from the Sun and Mars is 200 million km from the Sun.

1:7 subtract both vectors for short distance and add both for long distance and divide both short over long

The dependence of a metal's resistance on its length per unit area is shown. What is the resistivity of the metal?

2 × 10−8 Ω∙m Take the slope and you get ohms divided by (1/m) which gives ohm meters and that is resistivity of the metal find two points Y/X

Matter falling in the gravitational field of a central mass can form a hot, charged fluid. The fluid matter orbiting some stars radiates infrared light, but the matter orbiting black holes emits x-rays. Which of the following explains this discrepancy? The matter orbiting black holes must: A.be hotter than the matter orbiting stars. B.be colder than the matter orbiting stars. C.have lower kinetic energy than the matter orbiting stars. D.exhibit higher viscosity than the matter orbiting stars.

be hotter than the matter orbiting stars. Because the energy of x-ray radiation is greater than that of infrared radiation, the temperature of the matter orbiting black holes must be greater than the temperature of the matter orbiting the stars.

In the above figure, an LVAD pump is placed at one end of a "U"-shaped container, and a force gauge is placed at the other end. If the container is filled with an incompressible fluid, what is the ratio of the force measured by the force gauge to the force exerted by the LVAD? A.1:4 B.1:2 C.1:1 D.4:1

B.1:2 The ratio of the forces is equal to the ratio of their respective areas. According to the figure, the gauge area A2 is half the LVAD area A1 ( A2 = A1/2). Therefore, the force experienced by the force gauge is 1/2 the LVAD force, corresponding to a 1:2 ratio between the force at the force gauge and the force at the LVAD

mass flow rate

A mass flow rate refers to the quantity of fluid or solute mass that flows past a fixed point per unit time. For solutes uniformly dissolved within fluids, the mass flow rate of the solute is equal to the product of volumetric flow rate and mass concentration of the solute (ie, mass of solute per unit volume of fluid).

pitot tube

A pitot tube measures the velocity of air flow. The height of the fluid in the tube is proportional to the square of the air velocity at the opening on the side of the tube. h is proportional to vb^2

State and process functions

A system is in a state of thermodynamic equilibrium if the temperature of the system is constant and uniform throughout its volume and there is no flow of energy. A system is in thermodynamic equilibrium with another system or its surroundings if both have the same temperature. State functions (or state quantities) describe the equilibrium state of a system as a relationship between various thermodynamic variables and are independent of the path taken by the system to arrive at its present state. State functions include a system's pressure, volume, and temperature. Process functions (or path functions) describe the path taken by a system to transition from one equilibrium state to another. A system transitions from one state to another due to a net flow of energy in the form of heat transfer or work. For example, the loss or gain of heat is a process function because it describes the path taken by a system from its current pressure, volume, and temperature to a different set of values. In the Hampson-Linde cycle described in the passage, work is done by the compressor on the nitrogen gas to decrease its volume. Therefore, work is a process function because it describes what was done to the system to change its state (Choice C). A system's entropy is a measure of its current state of disorder and does not depend on how the system arrived at that state (Choice B). Therefore, the entropy of nitrogen is a state function. (Choice D) Although it is true that the work done by the compressor describes a path to an equilibrium state, work does not describe the state of the system. Therefore, work is a process function, not a state function. Educational objective: State functions describe the equilibrium state of a system as a relationship between various thermodynamic variables, and a process function describes the path taken by the system to go from one equilibrium state to another. Therefore, entropy is a state function, and work is a process function. State functions: pressure, density, temp, volume, enthalpy, internal energy U, Gibbs, Entropy Path functions: work, heat q

An ideal fluid flows within a fixed tube with decreasing cross-sectional area. Assuming constant height and volumetric flow rate, which of the following graphs best illustrates the relationship between fluid pressure and the increase in fluid velocity?

As velocity increases Pressure decreases

A star orbiting a black hole in the clockwise direction begins to slowly spiral inward due to a counterclockwise drag force. When the star's radial distance from the black hole is 1.0 × 106 km, a drag force of 250 N acts perpendicular to the orbit radius. What is the torque on the star? A.0 N∙m B.2.5 × 109 N∙m in the counterclockwise direction C.2.5 × 1011 N∙m in the clockwise direction D.2.5 × 1011 N∙m in the counterclockwise direction

D.2.5 × 1011 N∙m in the counterclockwise direction

mag in multi lens system

Magnification is the phenomenon in which a lens produces an image that is enlarged or shrunken relative to the original object. Multi-lens systems arranged in series provide a combined magnification equal to the product of all individual lens magnifications.

As the kinetic energy of the protons in the beam is increased, what happens to the average depth into the body that the protons penetrate? (Note: Assume the protons move in a straight line and slow down at a constant rate.) A.The depth decreases. B.The depth increases. C.The depth remains constant. D.The depth increases, then decreases.

The depth increases. The work-energy theorem implies that particles with greater kinetic energy penetrate deeper into a material such as body tissue.

v = wavelength / T

The wavelength is the distance over which a wave repeats, and the period is the time in which a wave repeats. Wave speed can be determined by dividing the wavelength by the period.

A car drives at a constant speed toward the wall of a canyon while sounding its horn at a particular frequency. The sound waves from the horn reflect from the canyon wall and return to the car as it continues moving toward the wall. What happens to the period of the reflected waves observed by the driver of the car? A.The period of the reflected waves will remain the same because the returning waves travel the same speed as the outgoing waves. B.The period of the reflected waves will remain the same because the speed of the car is constant. C.The period of the reflected waves will decrease because the observer moves in the opposite direction from the waves. D.The period of the reflected waves will decrease because the speed of the returning waves is increased.

The period of the reflected waves will decrease because the observer moves in the opposite direction from the waves. According to the Doppler effect, the wave period measured by an observer depends on the relative motion of the source creating the wave (eg, sound) and the observer. For example, when the observer and a source emitting waves of period T0 move toward each other, the observed wave period Tobs is smaller than T0. A smaller period is observed because the source has moved closer to the observer and the measured time between emitted wave crests is reduced. Conversely, when the source and the observer move away from each other, Tobs is greater than T0 because the waves emitted from the source travel a longer distance to the observer. The period of an observed wave changes based on the relative motion between the source and the observer. When source and observer move toward each other, wave period is decreased.

v = fλ

The speed of sound is equal to the product of the wavelength and frequency of the sound waves. When sound travels through different mediums, its speed and wavelength may change, but the frequency remains constant.

s = 1/f

The strength S of a lens is given in units of diopters (D), which is the inverse of meters. The lens strength equals the inverse of the focal length f of the lens: total strength: add them

During Experiment 2, the subject lifts a ball with a mass m a vertical distance d1 and then lowers the ball a greater vertical distance d2. What is the net work done by gravity on the ball? A.W = 0 for all cases because gravity is a conservative force B.W = mg(d2 − d1), because gravity does work to lift and lower the ball C.W = mgd2, because gravity does work only to lower the ball D.W = mg(d1 + d2), because gravity does work only on the net vertical path

W = mg(d2 − d1), because gravity does work to lift and lower the ball Gravity is a conservative force; it depends on the initial and final position of the mass it acts on. The net work W done by a conservative force is the amount of energy transferred by the force F over a displacement d in the direction of the force: W = Fd Work and displacement are positive if they are in the same direction as the force, and gravity does work only along the vertical axis; W is positive when the ball is lowered because gravity acts downward. The ball's net downward displacement is the difference between the lowered distance d2 and the raised distance d1: d = d2 − d1 W = F(d2 − d1) The force due to gravity on the ball is its weight, which is the product of its mass m and the acceleration due to gravity g: F = mg. Therefore, the net work done by gravity is W = mg(d2 − d1)

When dietary sodium intake increases, the electric current measured by a DSGR device also increases. Current increases because: A.blood pressure energy is converted into electric potential energy. B.the accumulation of positively charged ions causes blood glucose to precipitate. C.electrolytes within blood transport electric charge. D.alterations in red blood cell shape increase capacitance.

electrolytes within blood transport electric charge.

Researchers measured the pressure and volume changes in the hearts of volunteers. Which of the following graphs represent the greatest amount of work done by the heart?

in this question, W equals the product of the changes in pressure ΔP and volume ΔV, because the PV loops do not start at zero P or V: W=ΔP×ΔV A cardiac PV loop records the pressure and volume in the left ventricle during a complete cardiac cycle. The area enclosed by the PV loop represents the work done by the heart. The one with largest area

A fluid is stirred until it becomes turbulent. After the stirring stops, the fluid gradually returns to its original static state. The turbulent flow does not continue indefinitely because: A.the fluid is incompressible. B.the kinetic energy in the flow is transferred to gravitational potential energy. C.the energy put into the flow by stirring is transferred by convection. D.the energy put into the flow by stirring is dissipated by the fluid's viscosity.

the energy put into the flow by stirring is dissipated by the fluid's viscosity. As a static fluid is stirred up, energy is transferred into the kinetic energy associated with the motion of the fluid. At first, the flow is laminar but it eventually becomes turbulent as the velocity of the fluid increases. In a turbulent flow, the velocity varies dramatically from point to point. Once the stirring stops, the only force acting on the flow is the viscous shearing force resulting from the velocity gradients present within the fluid. Consequently, the kinetic energy of the flow is dissipated by frictional shearing forces such that the velocity decreases and the fluid gradually returns to a steady state.

According to the data in Figure 2, what is the spring constant k for normal bone? A.7.5 kN/mm B.10 kN/mm C.30 kN/mm D.40 kN/mm

10 kN/mm Displacing an elastic object from its equilibrium point (ie, its position at rest) generates an elastic force (Fel) that counteracts the force displacing the object. The elastic force acts to restore the elastic object to its original position if other forces acting on the object are removed. Hooke's law describes the elastic forces of perfectly elastic materials. It states that Fel is a function of object displacement (x) and the material's spring constant (k), which is a measure of the relative elasticity (stiffness) of a spring-like object: Fel=−kx In practice, most elastic objects are imperfectly elastic, and minimally or maximally displacing an imperfectly elastic, spring-like object from its equilibrium point generates an elastic force greater or less than that predicted by Hooke's law. As a result, Hooke's law must be applied cautiously to elastic materials to avoid error.

Assuming that the size and shape of red blood cells are uniform, by what factor would the quantity of red blood cells need to change to raise the capacitance of a blood sample to 250% of its original value? A.2/5 B.(2/5)2 C.5/2 D.(5/2)2

5/2 A parallel plate capacitor stores electrical charge (Q) on two equally but oppositely charged regions separated by some distance (d). Capacitance (C) is equal to the ratio of Q and the voltage (V) across the capacitor. Furthermore, because V equals the product of electric field strength E and d, it follows that C is inversely proportional to d: C=QV=QE⋅d⟹C∝1dC=QV=QE⋅d⟹C∝1d Capacitance also depends on the physical dimensions of each plate, because a higher Q can be stored without generating repulsive electric forces with a larger plate area (A). Hence, C is also directly proportional to A: C∝AC∝A Therefore, the overall proportionality expression relating capacitance to area and distance is: C∝AdC∝Ad In the context of DSGR, red blood cells act as a physical barrier that separates negatively charged electrons in the blood plasma from positively charged ions in the red blood cell cytoplasm. As a result, the cumulative surface area of the red blood cells in a blood sample is directly proportional to the total capacitance of the blood sample. Because the surface area of each red blood cell is generally considered to be fixed and uniform, increasing the capacitance of a blood sample requires increasing the quantity of red blood cells. Therefore, increasing the capacitance of blood to 250% (ie, 2.5 times its original value or by a factor of 5/2) would require increasing the quantity of red blood cells by a factor of 5/2. (Choice A) The capacitance of the blood is proportional to the total surface area of the red blood cells. Therefore, changing the quantity of red blood cells by a factor of 2/5 will decrease the capacitance to 40% of the original value, not increase the capacitance to 250% of the original value. (Choices B and D) The total surface area of the red blood cells is proportional to the number of red blood cells, not the square of the number of blood cells. Educational objective:The capacitance of a parallel plate capacitor is related to capacitor plate material, capacitor plate area, and the distance between plates. Capacitance is directly proportional to capacitor plate area and inversely proportional to the distance between plates.

Selected data points from a speed sensor in a crash test dummy's head during a collision are plotted in the figure shown. What does the slope of the plot, denoted by the dashed line, represent? A.Acceleration of the head B.Displacement of the head C.Kinetic energy of the head D.Work done on the head

Acceleration of the head When the plot of v versus t is not a simple straight line, the slope of the graph at each point in time is the same as the slope of the tangent line at that point. This instantaneous slope equals the instantaneous acceleration. In this question, data representing v of the dummy's head is plotted against t. The slope at each time point corresponds to the slope of the tangent line, shown as the dashed line in the figure. The slope of the tangent line is equal to the ratio of Δv and Δt, which is the same as the instantaneous a of the head at 5 ms:

A mirror is placed at the back of the block during the experiment. The laser light from the Doppler sensor reflects off the mirror, as shown in the diagram below. (Note: The figure is NOT drawn to scale.) Which of the following equations is true for any value of the incident angle, θ2?

All surfaces reflect light. Rough surfaces, such as a person or a tree, reflect light in all directions. A very smooth surface, such as a mirror, only reflects light in one specific direction. For a mirror, the reflected angle θR of the light is equal to the incident angle θI of the light, with the angles measured relative to a line perpendicular to the surface of the mirror (ie, the normal to the surface): θI=θR In this question, θI of the light is θ2 and θR is θ3. Therefore, θ2 is always equal to θ3.

Which group of blood vessels is the main source of peripheral resistance? A.The arteries, because they cause the greatest pressure fluctuations B.The arterioles, because they experience the largest pressure drop C.The capillaries, because they have the smallest vessel radii D.The venules, because they decrease blood pressure to its minimum

B.The arterioles, because they experience the largest pressure drop Equation 1 is an example of Ohm law for flow, which states that the pressure drop (ΔP) across a pipe (or vessel) is directly proportional to its resistance (R): ΔP = Q × R where Q is the volumetric flow rate. In other words, a relatively high pressure is required to drive flow through highly resistive vessels. Therefore, the group of vessels that has the greatest pressure drop across its entire length has the greatest resistance and is the main source of peripheral resistance. From the blood pressure profile of different vessels (Figure 3), the greatest pressure drop is seen across the arterioles. In addition to having the greatest vascular resistance, the arterioles are also one of the main regulators of blood pressure. Unlike other vessels, the arterioles are very muscular and can significantly change their vessel radii. By constricting or relaxing, these vessels can change the total peripheral resistance to maintain blood pressures as necessary. (Choice A) These pressure fluctuations seen in the large arteries are not due to the resistance of the vessel. The pressure within the vessel fluctuates between its systolic and diastolic pressure depending on whether the heart is contracting or relaxing. (Choice C) Although the capillaries have the smallest vessel radii and high individual resistances, they are the most numerous and are in parallel with each other. Therefore, the equivalent resistance of the parallel network of capillaries is relatively small. (Choice D) Vascular resistance depends on the pressure drop across a vessel, not the pressure at its end. Educational objective:From Ohm law for flow (ΔP = Q × R), the pressure drop across a vessel is proportional to its resistance. Therefore, the group of vessels with the greatest pressure drop across its length, the arterioles, is the main source of peripheral resistance.

Which of the following expressions gives the magnitude of the work done by the frictional force F if the synthetic skin and the load slide down the entire length L of the ramp and then are pushed back up to their original position? A.0 B.(F)(L) C.(F)(2L) D.(F)(3L)

C.(F)(2L) The work done by a conservative force (eg, gravity, electrostatic) depends on the net displacement (not distance) the force is applied. Because there is no net displacement in this case, the work done by gravity would be zero. However, friction is not a conservative force. Educational objective:Friction is a nonconservative force, which does not conserve the total mechanical energy (potential plus kinetic) in a system. The magnitude of the work W done by a nonconservative force depends on the total distance d through which the force F is applied: W = Fd.

Which of the following best describes the type of heat transfer that occurs in the external cooler of the Hampson-Linde cycle apparatus?

Conduction occurs as the coil of the external cooler gains heat from nitrogen gas. Heat is the energy transferred from one object to another due to their temperature difference, and it always flows from hotter objects to colder objects. Heat can be transferred by three different mechanisms: Conduction is the transfer of heat through direct physical contact. Convection is the transfer of heat through the flow of fluids. Fluids absorb heat from hotter regions and deliver it to colder regions. Radiation is the transfer of heat through electromagnetic radiation, such as infrared light. Radiation heat transfer is significant only for high temperatures. As the nitrogen gas flows through the coil of the external cooler, it transfers energy obtained during the compression stage to different sections of the coil. Therefore, the heat transfer results from the physical contact of the nitrogen gas and the coil and is primarily a conductive transfer of heat. (Choice A) Because heat is transferred from hotter objects to colder objects, heat is gained (not lost) by the dry ice. (Choice B) Both dry ice and the coil are solids. Therefore, these substances cannot participate in convective heat transfers. (Choice D) Because heat is transferred from hotter objects to colder objects, heat is lost (not gained) by the nitrogen. Educational objective: Heat is energy that flows from high temperatures to low temperatures. Heat can be transferred through direct physical contact (conduction), through the flow of fluids (convection), or through emission of electromagnetic energy (radiation).

volumetric flow rate Q

Fluid flow describes the motion of liquid or gas molecules. For a fluid traveling through a closed conduit (eg, pipe), the volume of fluid flowing past a fixed point per unit time is the volumetric flow rate (Q). Q is equal to the product of the velocity of the fluid (v) and the cross-sectional area (A) of the conduit at a given point: Q=A⋅v

A scientist studying capillary fluid exchange in a laboratory environment can most effectively increase the net fluid filtration out of the capillaries by doing which of the following? A.Increasing the speed of blood flow B.Increasing interstitial hydrostatic pressure C.Replacing blood with a less viscous fluid D.Decreasing blood osmotic pressure

D.Decreasing blood osmotic pressure The movement of fluid into and out of capillaries is important in both physiology and disease. The semipermeable membrane separating capillaries from surrounding tissue (ie, the interstitial space) permits the movement of fluid between these compartments. Consequently, net fluid filtration (Jv) is determined by the hydrostatic and osmotic pressure within each compartment, where a (usually) positive Jv indicates net movement of fluid out of the capillary. Hydrostatic pressure is created by fluid columns irrespective of spatial orientation (eg, blood vessels throughout the body). Fluid moves away from areas of high hydrostatic pressure and toward areas of low hydrostatic pressure. Consequently, capillary hydrostatic pressure (Pc) promotes the movement of fluid out of capillaries, whereas interstitial fluid hydrostatic pressure (Pif) diminishes the movement of fluid out of capillaries. Net fluid filtration is related to the difference in hydrostatic pressures as: Jv∝(Pc−Pif)�v∝�c-�if Osmotic pressure (Π) is created during osmosis by the diffusion of solvent across a semipermeable membrane separating compartments with different solute concentrations. Fluid moves from areas of low osmotic pressure to areas of high osmotic pressure, which is relevant to blood vessel physiology because the osmotic pressure of blood is greater than the osmotic pressure of interstitial fluid. The Starling equation can be used to calculate net fluid filtration and relates membrane permeability (K) to hydrostatic and osmotic pressure within the capillary and interstitial space: Jv=K[(Pc−Pif)−(Πc−Πif)]�v=��c-�if-��-�if Therefore, only a decrease in the osmotic pressure within the capillary Πc (eg, reduced concentration of plasma proteins or salts) would result in a further net positive Jv, increasing the movement of fluid out of the capillary. (Choices A and C) Increased blood speed or decreased blood viscosity would both result in greater volumetric blood flow. This would reduce blood hydrostatic pressure and decrease net fluid filtration (ie, less fluid moves out of the capillary). (Choice B) Increasing the interstitial hydrostatic pressure inhibits the movem

Ideal fluid

Fluids are substances that have no fixed shape and readily conform to the dimensions of the container in which they are placed. Fluids that are considered ideal share the following attributes: No viscosity: Friction between fluid molecules is negligible such that applied shearing forces (ie, gravity acting on a fluid pouring out of a glass) cause instantaneous, uniform acceleration of the fluid (Choice C). Laminar flow: The fluid flow is smooth, flowing in parallel layers with no interaction between each layer. In a pipe the fluid elements travel in straight lines and do not swirl around each other (Choice A). Incompressible: The density of the fluid is modified by neither external forces nor its own weight when oriented in a fluid column (Choice D). Ideal fluid behavior serves as a model for many practical applications of fluids. For example, water and mercury are both relatively incompressible, which allows both fluids to be used within a simple fluid barometer to reliably measure atmospheric pressure (Patm). Furthermore, ideal fluid behavior is essential for the application of Bernoulli's equation, which mathematically describes the conservation of energy in fluids in terms of fluid pressure (P), density (ρ), and velocity (v) between two points (A and B) within a conduit (ie, the container through which a fluid flows): PA+ ρghA+12ρ(vA)2=PB+ρghB+12ρ(vB)2�A+ ρ�ℎA+12ρ�A2=�B+ρ�ℎB+12ρ�B2 Bernoulli's equation predicts changes in fluid flow and pressure that occur following a change in fluid height (h) or conduit geometry. For example, Bernoulli's equation dictates that the pressure of an ideal fluid will decrease as fluid velocity increases and the height remains constant. Consequently, changes in fluid kinetic energy must be accompanied by changes in pressure energy so that overall energy is conserved. Therefore, the statement that fluid pressure is not influenced by fluid velocity is not true for an ideal fluid. Educational objective:Ideal fluids are totally nonviscous and incompressible; they exhibit smooth, laminar flow without viscosity. Bernoulli's equation dictates that an increase in the velocity of an ideal fluid is accompanied by a decrease in fluid pressure.

A train is traveling west at a velocity of 25 m/s. Another train is traveling east directly toward the west-bound train at a velocity of 15 m/s. The west-bound train blows its whistle with a frequency of 600 Hz when the two trains are 1000 m apart and then blows its whistle again 10 seconds later. For passengers on the east-bound train, how will the perceived frequency of the first whistle compare with the perceived frequency of the second whistle? (Note: Use 350 m/s for the speed of sound in air.) A.It will be 60% higher than the frequency of the second whistle. B.It will be 40% higher than the frequency of the second whistle. C.It will be approximately identical to the frequency of the second whistle. D.It will be 40% lower than the frequency of the second whistle.

It will be approximately identical to the frequency of the second whistle. The Doppler frequency shift depends on the velocities of the source and observer but does not depend on the distance between them.

In the presence of an external magnetic field (not shown), a proton initially traveling upward is deflected into the path labeled as A in the following figure. An electron with the same initial velocity as the proton travels through the magnetic field. What would be the expected path of the electron?

Particles with charge q and speed v are accelerated in a magnetic field B by the Lorentz force F, which has magnitude: F=qvB The direction of the force is determined by using the right-hand rule and is always perpendicular to the particle's velocity. As a result, the particle's trajectory is forced into a curved path. In the figure, the path of the proton is bent to the left in the presence of the external magnetic field. Consequently, the Lorentz force initially points to the left for positive charges in the magnetic field. However, because an electron is negatively charged, the trajectory of an electron would curve in the opposite direction, which is toward the right. Although the Lorentz forces on the proton and electron have identical magnitudes, their paths are determined by the acceleration a imparted on each particle. Newton's second law of motion implies that acceleration is inversely proportional to particle mass m: a=Fm=qvB Because the mass and inertia of an electron are much smaller than those of a proton, the electron experiences greater acceleration. Therefore, its path will have a greater curvature (Choice D). (Choices A and C) The trajectory of an electron would curve in the opposite direction (ie, toward the right). (Choice B) A particle with a negative charge and the mass of a proton would follow this path. Educational objective: The Lorentz force exerted on a moving charge in the presence of a magnetic field is perpendicular to the particle's velocity. As a result, the charge's trajectory is forced into a curved path, with negative charges and positive charges bent in opposite directions. Because an electron is less massive than a proton, an electron's path would be more curved in the same magnetic field.

In which of the following processes does energy convert from chemical energy to thermal and kinetic energy? A.Digesting a piece of bread B.Toasting a piece of bread C.Running a combustion engine D.Charging a cell phone with an external battery

Running a combustion engine According to the law of conservation of energy, energy cannot be created or destroyed, only transformed from one form to another. Combustion is a chemical process through which the chemical energy stored in the molecular bonds of the reactants is released by creating new bonds with less energy. The energy released from combustion is transformed into several forms. The combustion event produces a flash of light and a loud sound. The temperature of the gases increases (thermal energy), and the gases expand to move the engine's components (kinetic energy). Therefore, the conversion from chemical energy to thermal and kinetic energy takes place during the operation of a combustion engine.

heat energy q

The heat energy q generated by a resistor is proportional to its electric power P: q∝P =IV =V^2/R P equals the product of the current I and the voltage V across the resistor: P=IV The heat energy deposited in the body is proportional to the electric energy dissipated. The heat energy is related to the ratio of the voltage squared and the resistance. usually given voltage and resistance and asked to find ratio

Assuming the weight of the arm remains the same, how would the friction at the elbow change if the subject were to repeat the experiments 20 years later? A.The maximum static friction during Experiment 1 would increase. B.The kinetic friction during Experiment 1 would increase. C.The maximum static friction during the lifting motion in Experiment 2 would decrease. D.The kinetic friction during the lifting motion in Experiment 2 would decrease

The maximum static friction during Experiment 1 would increase. The passage states that cartilage degeneration increases with age, resulting in an increase in both the static and kinetic friction coefficients. Therefore, the older subject will experience increased static and kinetic friction at the elbow. Because the arm is stationary during Experiment 1, the maximum static frictional force would increase. (Choice B) Although kinetic friction is expected to increase due to cartilage degeneration, there is no movement in Experiment 1; therefore, there will be no kinetic friction.

Current in series and parallel

When resistors are arranged in series, charge conservation implies the same amount of current flows through each resistor. When resistors are arranged in parallel, Ohm's law implies the branch with the greater resistance has the lowest current.

A clinical study reports that the time required for the pulse wave to arrive at the kidney increases after renal artery ablation. A possible explanation for this could be that: A.

decreasing blood pressure causes the wavelength of the pulse wave to decrease.

When standing barefoot on a floor, body heat is transferred into the floor based on the thermal conductivity k of the flooring material. The heat flow rate per unit area H is defined by: where ΔT is the difference in temperature over a distance L. The tiled part of a floor in a room at room temperature feels colder than the carpeted part because: H = k delta T/L A.the temperature of the tile is lower than the temperature of the carpet. B.the thermal conductivity of the tile is higher than the thermal conductivity of the carpet. C.the thermal conductivity of the tile is lower than the thermal conductivity of the carpet. D.heat travels a greater distance through the carpet.

the thermal conductivity of the tile is higher than the thermal conductivity of the carpet. Heat is transferred from one location to another by the distinct processes of conduction, convection, and radiation. In conduction, intermolecular collisions cause the movement of heat between high- and low-temperature regions because molecules within high-temperature regions tend to move faster and therefore have larger kinetic energies. High-speed molecules impart kinetic energy by colliding with nearby slower-moving molecules, transferring thermal energy. As the cascade of intermolecular collisions continues, heat is transferred over a distance (L). The rate of heat transferred (H) from a high-temperature region (Th) to a low-temperature region (Tc) is directly proportional to the thermal conductivity (k) of the material adjoining them but inversely proportional to Thermal conductivity k measures how well a material transfers heat at a specified temperature gradient. For example, in metals, k is proportional to electrical conductivity (σ) because both conduction processes occur via the free electrons in a metal. For a person straddling the tile and carpet, the temperature gradient between the body (37° C) and each object is the same because the carpet and the tile are at the same temperature (room temperature 20° C). Heat flows from the warmer body to the cooler objects. However, tile is a better thermal conductor than carpet and therefore has a higher k. Consequently, heat transfer from the body to the tile is more rapid than the heat transfer to the carpet such that the person perceives the tile being colder than the carpet. (Choice A) Both the tile and the carpet are the same temperature, but the heat flow rate differs because tile has a higher k. (Choice C) If carpet had a higher thermal conductivity than tile, it would feel relatively cold to the touch. Instead, carpet feels warmer because it is more of a thermal insulator. (Choice D) Heat travels the same distance from the body into the tile and the carpet. However, the heat flow rate (and human perception of temperature) differs because tile has a higher k. Educational objective: The rate of heat transfer through conduction depends on the thermal conductivity of a substance. Objects at the same temperature but with different thermal conductivity are perceived to be different temperatures.

Compared to osteoporotic bone, the work required to compress normal bone by 2 mm is: A.3/4 as great. B.the same. C.4/3 times greater. D.8/3 times greater.

4/3 greater

A car moves in a straight line along a paved road. The velocity of the car versus time is shown: What is the displacement of the car from 0 s to 15 s? A.300 m B.400 m C.500 m D.600 m

400 m

Which of the following LED wavelengths would be suitable for use in a PPG system? 500 nm 630 nm 810 nm A.I only B.I and II only C.II and III only D.III only

500 and 630 only because visible light spectrum

The fundamental frequency of a glass tube is measured to be f when the tube is capped at one end, but open at the other end. What is the fundamental frequency of the tube when the end cap is removed and both ends are open?

2f Standing sound waves are generated in tubes due to interference between incident waves and reflected waves, which move in opposite directions in the air tube. The resonating sound waves in a pipe create nodes (ie, points of zero amplitude) at closed ends due to restricted air movement and antinodes (ie, points of maximal amplitude) at open ends due to free motion of air molecules. A pipe open on both ends will resonate at the fundamental frequency when antinodes are formed at each end. A pipe with one end open will resonate at the fundamental frequency when a node is formed at the closed end and an antinode is formed at the open end. In this question, the glass tube is initially closed c at one end and then open o at both ends. At the fundamental frequency, the wavelengths of sound are twice and four times the tube length L: λo=2Lλo=2� λc=4Lλc=4� Therefore, λc=2λ0λc=2λ0 The wave speed v is the product of the wavelength λ and frequency f of a wave: v=λf�=λ� Because the speed of sound is constant in the tube: vo=vc�o=�c foλo=fcλc�oλo=�cλc foλo=fc(2λo)�oλo=�c2λo fo=2fc�o=2�c Therefore, the fundamental frequency of the glass tube when open at both ends is twice that of the fundamental frequency when the tube is closed at one end. (Choice A) f/4 is the result of an error made by plugging in the wavelength for a closed-end tube into wave speed equation (f = v/4L). (Choice B) f/2 would be correct if the question instead asked for the fundamental frequency of the tube closed at one end. (Choice C) f would be true if the tube length changed to maintain the same fundamental frequency. Educational objective: The fundamental frequency of standing sound waves in a tube of fixed length depends on whether the pipe is open at both ends or closed at one end.

Light can be scattered as it travels through tissue, resulting in different path lengths from the LED to the detector. The LED generates light at 600 nm. This wavelength leads to destructive interference when the path lengths differ by: A.150 nm B.300 nm C.600 nm D.1,200 nm

300 nm When two waves meet at the same point, they overlap with one another and cause wave interference. Pure constructive interference occurs when the peaks and troughs of the two waves overlap exactly, meaning the phase difference between the waves is 0°. This corresponds to a path length difference Δd between the two waves of zero or an integer multiple of the wavelength λ: Δd=0,λ,2λ,3λ,...∆d=0,λ,2λ,3λ,... When the peaks of one wave overlap exactly with the troughs of the other wave, the phase difference between the waves is 180° and pure destructive interference occurs. This happens when the difference in path length is half the wavelength or an odd multiple of half the wavelength: Δd=λ2,3λ2,...∆d=λ2,3λ2,... In this question, the wavelength is 600 nm and destructive interference occurs when the path length difference is 300 nm, 900 nm, 1,500 nm, and so on. When the difference in the path lengths is 300 nm, the sum of the two waves yields a zero signal consistent with destructive interference. (Choice A) A difference in path length of 150 nm is one fourth of the wavelength, yielding a phase shift of 90°. Summing two waves shifted by 90° results in a combination of both constructive and destructive interference. (Choices C and D) Differences in path length of 600 nm or 1,200 nm are multiples of the wavelength, yielding a phase shift of 360° and pure constructive interference. Educational objective:Destructive interference occurs when the path lengths of two waves differ by half the wavelength. Differences in path length that are integer multiples of the wavelength cause constructive interference.

The diameter of a segment of an artery is reduced by a factor of two due to an obstruction. Assume that the flow is incompressible and laminar, and therefore follows the continuity equation. Compared to an unobstructed segment of the artery, the velocity of blood in the obstructed segment of the artery is:

4 times as large. The continuity equation expresses the conservation of mass observed as fluids flow through a conduit. The continuity equation indicates that velocity is inversely proportional to the square of diameter.

Circularly polarized light results from the vector sum of the electric field oscillations of two linearly polarized transverse waves traveling along the same axis. To achieve circular polarization, the two transverse waves must be out of phase to one another. The necessary phase difference is: A.0° B.90° C.180° D.360°

90 Polarization is a property unique to transverse waves (eg, electromagnetic radiation) in which the wave oscillations are aligned in a particular spatial orientation within the x,y,z-coordinate system. When two polarized waves combine, a new wave is formed with a different polarization. For example, a wave polarized along the x-axis totally in-phase with a wave polarized along the y-axis produces a combined wave that is polarized between the x- and y-axes at a 45° angle. When the polarization of a combined wave rotates around the axis of propagation, the wave is said to be circularly polarized. If the polarization of the combined wave rotates in a clockwise direction when viewed facing the direction of propagation, the waveform is right-polarized; if the polarization rotates in a counterclockwise direction, the waveform is left-polarized. Circular polarization occurs when two wave forms with equal amplitude and perpendicular linear polarization (ie, polarized along different axes) propagate 90° out of phase to one another (ie, one waveform yields zero displacement when the other waveform is yielding a peak or a trough). The mismatch in phase causes each contributing wave to generate momentary oscillations that are different at every point in time. This results in a continuous rotation in the orientation of the combined wave. A 90° phase difference is required for circular polarization because only a 90° phase shift yields both the positive and negative oscillations along each axis and the symmetry necessary to produce a circular polarization pathway. (Choices A and D) Phase differences of 0° and 360° both reflect waveforms that are traveling completely in phase with one another. The polarization of two waves traveling in phase with one another is fixed and will not rotate. (Choice C) A phase shift of 180° represents waves traveling completely out of phase and will result in a polarization oriented in a fixed orientation at a 45° angle to the axis of polarization of each contributing wave. Educational objective:Circular polarization refers to the rotation of polarization observed when two transverse waves with equal amplitude and perpendicular linear polarization propagate out of phase with one another

If a liquid is at its exact boiling point, what will happen to the liquid when a small amount of heat is added to it? A.None of the liquid will turn to gas, and the temperature will increase. B.All the liquid will turn to gas, and the temperature will remain the same. C.A small amount of the liquid will turn to gas, and the temperature will increase. D.A small amount of the liquid will turn to gas, and the temperature will remain the same.

A small amount of the liquid will turn to gas, and the temperature will remain the same. Matter typically exists in one of three phases: solid, liquid, or gas. Matter transitioning from one phase to another undergoes a phase change in which it absorbs or releases heat until all the matter completes the transition to the new phase. During a phase change, the temperature of the material remains constant even though heat is added or removed. Matter transitions from a liquid to a gas at its boiling point and requires the addition of heat energy equal to its heat of vaporization for all the liquid to transition into gas. In this question, the temperature of the liquid equals its exact boiling point. As a result, adding a small amount of heat will cause some of the liquid to transition into gas, but the temperature will not change. (Choices A and C) The temperature will remain constant until the heat of vaporization is exceeded and all the liquid has turned to gas. (Choice B) A small amount of heat will convert a small amount of the liquid to gas, not all the liquid. Educational objective: During phase transitions, the temperature of a substance remains constant. A liquid at the exact temperature of its boiling point is transitioning from a liquid to a gas. It must gain an amount of heat equal to its heat of vaporization before all the liquid turns to gas and the temperature increases.

Thermodynamic processes

A system is in a state of thermodynamic equilibrium if the temperature of the system is constant and uniform throughout its volume and there is no flow of energy. A system is in thermodynamic equilibrium with another system or its surroundings if both have the same temperature. State functions (or state quantities) describe the equilibrium state of a system as a relationship between various thermodynamic variables and are independent of the path taken by the system to arrive at its present state. State functions include a system's pressure, volume, and temperature. Process functions (or path functions) describe the path taken by a system to transition from one equilibrium state to another. A system transitions from one state to another due to a net flow of energy in the form of heat transfer or work. For example, the loss or gain of heat is a process function because it describes the path taken by a system from its current pressure, volume, and temperature to a different set of values. In the Hampson-Linde cycle described in the passage, work is done by the compressor on the nitrogen gas to decrease its volume. Therefore, work is a process function because it describes what was done to the system to change its state (Choice C). A system's entropy is a measure of its current state of disorder and does not depend on how the system arrived at that state (Choice B). Therefore, the entropy of nitrogen is a state function. (Choice D) Although it is true that the work done by the compressor describes a path to an equilibrium state, work does not describe the state of the system. Therefore, work is a process function, not a state function. Educational objective:State functions describe the equilibrium state of a system as a relationship between various thermodynamic variables, and a process function describes the path taken by the system to go from one equilibrium state to another. Therefore, entropy is a state function, and work is a process function.

A monoatomic ideal gas is initially sealed within a container featuring a piston fixed in place at one end. The piston is then unlocked and allowed to move under constant pressure. How does the initial heat capacity of the gas at constant volume CV compare with the heat capacity of the gas at constant pressure CP and why? A.CP will be greater than CV, because the gas can expend energy by doing work on the piston. B.CP will be less than CV, because the movement of the piston will prevent heat transfer. C.CP will equal CV, because the internal energy of the gas can no longer change. D.CP will equal CV, because the gas molecules are monoatomic and ideal.

A.CP will be greater than CV, because the gas can expend energy by doing work on the piston. Therefore, allowing a previously fixed piston to move freely (to maintain constant pressure) will increase the molar heat capacity of a monoatomic ideal gas. (Choices B, C, and D) Heat may transfer into or out of the gas and change the temperature and internal energy of the gas whether the piston is allowed to move or not. However, once the piston becomes mobile, work can occur. As a result, the heat capacity cannot remain constant but will increase. Educational objective:The molar heat capacity of a gas is the amount of heat required to raise the temperature of 1 mole of the gas by 1 degree Kelvin. The molar heat capacity of a gas at constant pressure exceeds the molar heat capacity of a gas at constant volume.

A voltmeter is used to measure the voltage across RB in Figure 1 after the switch is closed. Which of the following best describes the electrical properties of the voltmeter? A.It has a very large resistance. B.It has a resistance similar to RB. C.It draws a very large current. D.It draws a current similar to RB.

A.It has a very large resistance. A voltmeter measures the voltage V between two points in an electric circuit. To measure V across a resistor, the voltmeter is connected in parallel with the resistor because circuit elements connected in parallel have the same V. By Ohm's law, the resistor's V equals the product of the current I and the resistance R: V=IR To achieve an accurate measurement of V, connecting the voltmeter to the circuit should not alter the current through the resistor. In this question, the voltmeter measures V across RB and should not affect the current I through RB. However, a voltmeter with a low resistance will draw a large current, decreasing the I through RB. Consequently, the voltmeter will affect the circuit and measure a lower V across RB. Therefore, the voltmeter should have a very large resistance to minimize any changes to I through RB. A voltmeter with a very large resistance behaves like an open circuit (ie, no current flows through the voltmeter) when it is connected to a circuit. (Choice B) If the voltmeter's resistance is similar to RB, some of the current that should flow through RB instead flows through the voltmeter, and the voltage measured across RB is lower than the true value. (Choices C and D) If the voltmeter draws either a large current or a current similar to RB, the current through RB is reduced and the voltage measured across RB is lower than the true value. Educational objective: A voltmeter is connected in parallel with a circuit element to measure its voltage. The voltmeter should behave like an open circuit (ie, have a very large resistance) to ensure accurate voltage measurements.

What additional information do the researchers need from the crash test dummy to estimate the power of the collision in the experiment shown in Figure 2? A.Mass of the head B.Time until the head stops moving C.Tension of the neck during the collision D.Velocity of the head at the end of the collision

A.Mass of the head Power (P) is the rate of work (W) per unit time (t), and work is the energy transferred by a force through a distance. From the work-energy theorem, work is equal to the change in the kinetic energy (KE) of an object. Therefore, power can be calculated from ΔKE and t: P=Wt=ΔKE/t An object's kinetic energy is the energy associated with its motion, and it is calculated from its mass m and velocity v: KE=1/2mv2 Therefore, the power of the collision shown in Figure 2 can be determined from its ΔKE, which depends on the head's mass and its initial and final velocities during the collision. The head is stated to be stationary initially, and the final velocity of the head can be determined from the information given in Figure 2 (Choice D). Therefore, the mass of the head is needed in addition to the given information to determine the power of the collision. (Choice B) The power of the collision is determined from the duration of the collision. The time until the head stops moving may occur after the collision has ended. (Choice C) Tension is the force experienced by a string (or similar object) due to opposing forces at each of its ends. The forces at the neck do not need to be known to estimate the power of the collision. Educational objective:Power is the rate of work per unit time, and work is equal to the change in the kinetic energy of an object. Kinetic energy is due to motion, and it is calculated from an object's mass and velocity: KE=12mv2

Does blood flow to the skin increase during exercise? A.Yes, because regulation of body temperature is improved B.Yes, because blood supply to skeletal muscles is improved C.No, because blood supply to skeletal muscles is reduced D.No, because cardiac output is reduce

A.Yes, because regulation of body temperature is improved During exercise, blood flow to the skin increases to maintain normal body temperature. Excess body heat generated during exercise can be transferred to the surface through convection and dissipated into the environment through radiation.

In the MS-MS separation chamber, the direction of the magnetic force on a moving ion is: A.perpendicular to both the ion's velocity and the direction of the magnetic field. B.perpendicular to the ion's velocity and parallel to the direction of the magnetic field. C.parallel to both the ion's velocity and the direction of the magnetic field. D.parallel to the ion's velocity and perpendicular to the direction of the magnetic field.

A.perpendicular to both the ion's velocity and the direction of the magnetic field. The Lorentz force is the force exerted on a moving charge in the presence of an electric field E and a magnetic field B. Electric and magnetic fields are known as vector fields; both quantities include magnitude and direction. The Lorentz force for a particle with a charge q and velocity v in an electric field E and magnetic field B is: F⇀=q(E⇀+v⇀×B⇀) The quantities F, E, v, and B are denoted as vector quantities. Because there is no electric field (E = 0) in the MS-MS separation chamber, the Lorentz force is simplified for the presence of a magnetic field only: F⇀=q(v⇀×B⇀) The quantity v⇀×B⇀�⇀×�⇀ is the cross product of the vectors v⇀�⇀ and B⇀�⇀. The cross product of two vectors is a vector perpendicular to both vectors. Therefore, the direction of the magnetic force is perpendicular to both the ion's velocity v and the direction of the magnetic field B. The specific direction of a cross-product vector can be determined through the right-hand rule. (Choice B) The force due to an electric field is parallel to the direction to the electric field, but the force due to a magnetic field is perpendicular to its field. (Choices C and D) If the magnetic force were parallel to the ion's velocity, the ion would accelerate linearly and not be forced into a curved trajectory. Educational objective: The Lorentz force equation is used to determine the force exerted on a charge in the presence of an electric field and a magnetic field. The force exerted on a moving charge due to a magnetic field is perpendicular to both the ion's velocity and the direction of the magnetic field.

When a stationary head is hit by a moving projectile, a contrecoup injury is likely to occur due to: A.the inertia of the brain. B.the weight of the skull. C.the center of mass of the head. D.the potential energy of the projectile.

A.the inertia of the brain. A contrecoup injury is described in the passage as a brain injury that occurs on the side of the head opposite an impact. This form of brain injury involves the movement of the brain relative to the skull due to the rapid acceleration and deceleration of the head. When a stationary head is hit by a moving object, the skull and the brain are both accelerated in the same direction. Because the brain can move within the skull, the brain will continue to move due to its inertia even after the skull had slowed significantly or stopped. An object's inertia is proportional to its mass, and it is the tendency of an object to resist changes to its speed; an object in motion will stay in motion, and an object at rest will stay at rest (Newton's first law). Therefore, the inertia of the brain can lead to a brain-skull collision on the opposite side of the head from the initial impact (contrecoup injury). (Choice B) An object's weight is the gravitational force exerted on its mass. The weight of the skull does not cause the continued relative motion of the brain within the skull. (Choice C) An object's center of mass is the average position of its distribution of mass. The head's center of mass changes as a result of the movement of the brain within the skull, but the center of mass itself is not responsible for the movement of the brain. (Choice D) An object's potential energy is its "stored" energy due to its height above the ground. The potential energy of the projectile does not cause the continued movement of the brain relative to the skull. Educational objective:An object's inertia is its resistance to changes in its velocity; objects tend to stay in motion or stay at rest. Due to the brain's inertia, the brain can continue to move independently of the skull and result in a contrecoup injury.

Given the relationship between vascular resistance and blood pressure decay in Equation 1, which of the following blood vessel categories has the greatest total vascular resistance during systole? (Note: Vessel arcades are comprised of multiple individual blood vessels.) A.Aorta B.Arterial arcade C.Venous arcade D.Superior mesenteric artery

Arterial arcade remember you were given the pressures on a graph with their +/- values. The pressure with the greatest +/- had the greatest change in pressure difference and R = P/Q so they are directly related and we were asked to find the greatest resistance Vascular resistance is the resistance in a blood vessel that must be overcome for blood to flow. Equation 1 can be rearranged to R = ∆P/Q, showing resistance R is directly proportional to pressure difference ∆P and inversely proportional to flow rate Q. Q must be the same for each vessel because the continuity equation states that the same volume of blood per unit time must flow through all the vessels that are connected in parallel. Thus, R is dependent only on ∆P, and the vessel with the greatest ∆P has the greatest R. All pressure measurements in the study were recorded during systole, the point of greatest pressure. Therefore, the pressure drop across a vessel is the difference between its pressure and the pressure of the next vessel. These pressure differences are calculated using Figure 2. The systolic pressure at the beginning of the arterial arcade is 78 mmHg and it drops to 17 mmHg at the next vessel, the venous arcade, and ∆P for the arterial arcade is 61 mmHg, which is greater than ∆P for any other vessel. Therefore, the arterial arcade has the greatest R. (Choice A) Although the aorta has the highest pressure, ∆P between the aorta and the next vessel, the SMA, is only 6 mmHg. Therefore, the aorta has a lower R than the arterial arcade. (Choice C) ∆P between the venous arcade and the next vessel, the SMV, is only 7 mmHg. Therefore, the venous arcade does not have the greatest R. (Choice D) ∆P between the SMA and the next vessel, the arterial arcade, is only 37 mmHg. Therefore, the SMA does not have the greatest R. Educational objective: The vascular resistance of a vessel is directly proportional to the pressure difference and inversely proportional to the volumetric flow rate. When the volumetric blood flow rate is the same in two vessels, the vessel with the greater pressure difference has the greater resistance to flow.

According to the passage, which of the following changes occurs as an astronaut leaves Earth's surface and enters orbit? A.Coefficient of kinetic friction between the astronaut and nearby objects. B.Astronaut center of mass. C.Astronaut bodily inertia. D.Magnitude of the gravitational force between the astronaut and the spacecraft.

Astronaut center of mass. In the case of a body with a non-uniform mass distribution (eg, humans), the CM is closer to the largest collection or concentration of mass. Furthermore, if a shift in mass occurs in one direction (ie, ri increases or decreases), the CM will also shift in the same direction. According to the passage, an orbit around Earth is a microgravity environment. In microgravity, PFS is observed as extracellular fluid previously contained within lower portions of the body (ie, feet and legs) shifts to the upper portions of the body (ie, chest and head). Consequently, the shift in an individual's fluid mass will result in a shift in the individual's center of mass. (Choice A) The coefficient of kinetic friction depends only on the properties of the two surfaces that are in contact. The friction force may change due to the effects of gravity on the normal forces between two objects, but the coefficient of friction remains constant. (Choice C) Inertia refers to an object's tendency to oppose changes in motion. Inertia depends only on the characteristics of the object itself (ie, mass), not on external factors such as gravity or position. (Choice D) The mass of the astronaut will not change upon entering low-earth orbit. Consequently, the magnitude of the gravitational force between the astronaut and nearby objects (eg, the spacecraft) will remain the same. Educational objective:The center of mass of a system of masses is the average of the masses weighted by their displacement from a fixed reference point. The center of mass shifts in the same direction as a redistribution of mass.

Which of the following experimental groups would aid in determining if the procedure described in the passage has a confounding variable? A.Group with laparotomy used without measuring blood pressure B.Group with minimally invasive aortic catheterization to measure mesenteric blood pressure C.Group fitted with noninvasive tail cuffs to measure systolic blood pressure D.Group with laparotomy to measure renovascular blood pressure

B.Group with minimally invasive aortic catheterization to measure mesenteric blood pressure *pick the one thats measuring the same thing as the study In an ideal experiment or study, any changes in the measured dependent variable are due to changes in the independent variable. However, this model may not be realistic due to confounding variables, uncontrolled variables that affect the dependent variable. If confounding variables cannot be eliminated, experiments should be designed to minimize their influence. To determine the magnitude of any effect of a possible confounding variable on the dependent variable, an experimental group that differs in the suspected confounding variable is tested. In the study described in the passage, different blood vessels of rats (independent variable) were accessed through an invasive laparotomy procedure (suspected confounding variable) to measure mesenteric blood pressures (dependent variable). The inclusion of an alternative procedure that is minimally invasive or noninvasive but still measures mesenteric blood pressures would determine if laparotomy were a confounding variable by finding differences in the measured blood pressures. (Choices A and D) The suspected confounding variable (procedural invasiveness of laparotomy) is not changed. In addition, the dependent variable (mesenteric blood pressure) should not change. (Choice C) Although the suspected confounding variable (procedural invasiveness of laparotomy) is changed by using a tail cuff, the dependent variable (mesenteric blood pressures) should not change. Educational objective: A confounding variable is an uncontrolled variable different from the independent variable but that still has an impact on the dependent variable. The effect of a confounding variable can be observed by including a group in an experiment that differs in the confounding variable.

If the student repeated the experiment by replacing the water in the calorimetry device with an ice bath at 0°C, how would the experimental results differ? A.The temperature of the water would increase to 10°C. B.The temperature of the water would begin to increase at a later time. C.The heat released when ice melts increases the measured temperature. D.The amount of heat released from the combustion reaction would increase.

B.The temperature of the water would begin to increase at a later time. At the melting (or freezing) point of a substance, the substance can exist in either its solid or liquid phase. Because the freezing/melting point of water is 0°C, the ice bath will remain as a mixture of solid ice and liquid water unless heat is added to or removed from the mixture. The latent heat of fusion (melting) is the amount of heat (energy) required to convert a solid at its melting point temperature to its liquid phase by breaking the bonds between the molecules in the solid phase. The heat released from the combustion reaction will first go toward the latent heat of fusion to melt the ice into liquid water. The temperature of the water will be constant at 0°C as long as ice is still present and will not start to increase until after all the ice melts. Therefore, the temperature of the water would begin to increase at a later time (compared to the original experiment) when enough heat is transferred from the combustion reaction to first melt the ice (latent heat of fusion). (Choice A) Because some of the heat released goes toward the latent heat of fusion of the ice to melt it, less heat will be available to increase the temperature of the water. Therefore, the magnitude of the temperature increase would be less than the 10°C temperature change in the original experiment. (Choice C) Ice absorbs heat when it melts. Conversely, liquid water releases heat equal to the latent heat of fusion when it freezes. (Choice D) The amount of heat released from the combustion would be unchanged because it depends on the mass of the reactants (powdered sample), which is unchanged. Educational objective:The phase transition from a solid to a liquid requires heat (energy) to break the bonds between molecules; this energy is the latent heat of fusion. When heat is added to a mixture of ice and water at 0°C, the heat will first go toward melting the ice before raising the temperature of the water.

The misdirected transmission of a high-voltage electrical current is associated with a risk of accidental fire. To eliminate the risk of such accidents, the type of material that must be applied to the surface of bare wires is known as: A.an electrical conductor. B.an electrical insulator. C.a thermal conductor. D.a thermal insulator.

B.an electrical insulator. Electrical conductivity is a physical property that describes how easily electric charge flows through a given material. In solids, electrical conductivity is closely related to how readily electrons can move between atoms to produce an electric current. Electrons within metals are weakly attracted to their corresponding nuclei because the atomic number of many metals is such that the distance between positively charged protons and negatively charged valence electrons is relatively great. Consequently, electrons within metallic materials may be easily dislodged following exposure to an external electric field. Therefore, most metals are electrical conductors whereas most nonmetals are electrical insulators (materials that do not readily transmit electrical energy). In many cases, electrical fires begin as combustible foreign materials enter the electrical circuit, accumulate thermal energy from the high voltage source, and ignite. To prevent such accidental fires, electrical wires are coated in with an electrical insulator with high resistance, which does not transmit electrical energy and prevents electric current from easily exiting the circuit. (Choice A) Electrical conductors are used to facilitate current because the electric field that must be applied to a highly conductive material is less than that required for other materials, which conserves electrical potential energy (ie, voltage). (Choice C) Many metals are also thermal conductors, meaning that they readily act to transfer thermal (heat) energy via conduction. Facilitating thermal energy transfers between nearby atoms and molecules will not prevent adverse electrical events like electrical fires. (Choice D) Many thermal insulators are materials in which atoms and molecules are relatively sparse (eg, foam), making the exchange of thermal energy through conduction difficult. Thermal insulation is used to maintain the temperature of a region or object, not to prevent electrical accidents. Educational objective: Electrical conductors facilitate electrical current (ie, the movement of charge) whereas electrical insulators inhibit current. Although some electrical conductors are also thermal conductors, mechanisms of thermal and electrical conductivity are not the same.

A speaker is at rest on a tabletop and produces a steady sound of constant frequency. A guitar is placed near the speaker. After some time, the speaker is turned off and a guitarist notices that one of the guitar strings is vibrating in a standing wave pattern. Which of the following statements about the standing waves on the guitar string is true? A.The frequency of the standing waves is lower than the frequency of the waves produced by the speaker because the sound waves lose energy before they reach the guitar string. B.The wavelength of the standing waves is shorter than the wavelength of the waves produced by the speaker because the sound waves lose energy before they reach the guitar string. C.Both waves have the same frequency because the standing waves on the string are a result of the sound waves produced by the speaker. D.Both waves have the same wavelength because the standing waves on the string are a result of the sound waves produced by the speaker

Both waves have the same frequency because the standing waves on the string are a result of the sound waves produced by the speaker. A wave is defined as perturbation that travels from one point to another. Mechanical waves (eg, sound waves, waves on a string) are perturbations created by oscillations in a medium such as air or a string. All waves are characterized by their wavelength, frequency, and amplitude. As a wave propagates, it carries energy from one location to another. The energy contained in a wave is directly proportional to the square of its amplitude but is independent of the wavelength and frequency. When a wave moves from one medium to another, the amplitude and wavelength change but the frequency of the wave remains constant. In this question, the speaker creates sound at a particular frequency. Sound is a mechanical wave formed by vibrations of air molecules. The energy in the vibrating air near the guitar creates a standing wave in the new medium of the guitar string with the same frequency as the sound but with a different amplitude and wavelength.

A researcher wants to increase the acceleration of protein samples during electrophoresis. Which of the following changes will increase the acceleration of the samples? (Note: Assume that the time the voltage source is on is constant, the samples do not actually reach the anode, and that friction is negligible during protein migration.) A.Increasing the number of protein molecules in the samples B.Increasing the distance between the anode and the cathode C.Decreasing the distance between the anode and the cathode D.Decreasing the voltage

C.Decreasing the distance between the anode and the cathode The acceleration of a protein during electrophoresis depends on the charge of the protein, the voltage, the anode/cathode distance, and the mass of the protein. Decreasing the anode/cathode distance increases the acceleration of the protein.

Ignoring any attachments between the spinal discs and vertebrae, how would the maximum force of static friction between these anatomical structures compare for a person standing on the surface of the Moon to a person standing on the surface of the Earth? A.It would be 6 times as great. B.It would be approximately equal. C.It would be 1/6 as great. D.It would be 0.

C.It would be 1/6 as great. Friction refers to the force that resists sliding between two surfaces. Friction negates (partially or completely) any forces that promote sliding. For example, static friction Ffr occurs when the frictional force is equal and opposite to the combination of forces promoting motion. The magnitude of Ffr increases until the forces promoting motion exceed the maximum value of Ffr and the two surfaces start to slide against each other. The maximum static friction force is equal to the product of the coefficient of static friction μs, and the normal force N, which is typically equal to the weight mg: Ffr=μsN=μsmgFfr=μsN=μsmg Within the spinal column, the N between the intervertebral discs and the vertebrae is equal to the weight of the body above the discs. Because both m and μs are intrinsic properties, they are not affected by situational factors such as gravity. Therefore, only a change in g will influence the maximum Ffr observed on the Moon relative to the maximum Ffr observed on the Earth. Specifically, the maximum value of Ffr on the surface of the Moon will be 1/6 the maximum value of Ffr on the surface of the Earth because g on the Moon is 1/6 the magnitude of g on the Earth.

An object is launched with a one-time burst of propulsion away from the surface of the Moon. After the burst, which of the following best describes the changes that occur as the object moves away from the Moon's surface? A.The object mass is dissipated as heat. B.Potential energy is converted into kinetic energy. C.Kinetic energy is converted into potential energy. D.Total mechanical energy is not conserved.

C.Kinetic energy is converted into potential energy. After the object (eg, a rocket) is launched from the Moon, the only force present in the system is gravity. As the rocket moves away, the gravitational force is oriented toward the Moon. Therefore, work done by gravity progressively decreases the velocity and the kinetic energy of the object: KEi>KEf Simultaneously, the potential energy of the object increases (becomes less negative) as the radial distance from the mass increases: PEi<PEf The decrease in the kinetic energy of the object is accompanied by an increase in the potential energy of the object such that conservation of energy is maintained. (Choice A) The mass of the object is independent of gravity, and no forces act on the object that would cause depletion of mass. (Choice B) After launch, the PE of the object increases while the KE of the object decreases. Therefore, PE could not have been transformed into KE. (Choice D) The total mechanical energy of the system is conserved because gravity is the only force acting on the object after it is launched (no drag force is present because the Moon has no atmosphere). Educational objective:Conservation of energy states that any change in kinetic energy is accompanied by an equal and opposite change in potential energy such that the total mechanical energy remains constant. The kinetic energy of an object launched upward in gravity is converted into gravitational potential energy.

The blood pressures of an artery in the neck and an artery in the leg of a person lying down are measured, and their difference calculated. When the blood pressures are taken after the person stands up, their difference: A.decreases because flow resistance is greater over horizontal distances. B.remains the same because blood is modeled as an ideal fluid. C.increases because viscous pressure acts in the direction of gravity. D.increases due to the hydrostatic pressure difference between the two locations.

D.increases due to the hydrostatic pressure difference between the two locations. At any point, the pressure exerted by the weight (potential energy) of a fluid is directly proportional to its depth; this pressure is known as hydrostatic pressure. The hydrostatic pressure difference ∆P between any two points in a fluid is found by ∆P = ρg∆h where ρ is the density of the fluid, g is the acceleration due to gravity, and ∆h is the vertical distance between the locations where the initial and final pressures are measured. When the person is lying down, the neck and the leg are at about the same height, making ∆h negligible. However, when the person stands up, the ∆h between the neck and the leg increases significantly. The blood pressure difference increases due to the hydrostatic pressure of the column of blood from above the leg to below the neck. (Choice A) From Equation 2, flow resistance is due to the viscosity of blood and the geometry of the vessel through which it flows. Flow resistance is independent of the direction of flow. (Choice B) An ideal fluid is one that possesses negligible viscosity, and an ideal fluid would still experience hydrostatic pressure. In addition, blood is not modeled here as an ideal fluid. (Choice C) Viscosity is a measure of a fluid's resistance to flow due to internal frictional forces; it is not a measure of pressure. In addition, viscosity acts in the direction opposite the flow. Educational objective: Hydrostatic pressure is the pressure exerted by the weight (potential energy) of a fluid. The hydrostatic pressure difference between two points in a fluid is proportional to the fluid's density, the gravitational acceleration, and the vertical distance between the two points.

increase in string tension

For constant wavelength, an increasing the string tension also increases wave speed and frequency. Higher frequency results in crests that are closer together on a graph of displacement as a function of time.

A steel tow cable is used to pull a car at a constant velocity toward a barrier during a crash test. What information about the test is needed to calculate the tension in the cable? Friction force on the car Mass of the car Velocity of the car

I only Mechanical equilibrium occurs when the net external force acting on an object is equal to zero. This does not imply that no forces are acting on the object, but rather that all forces acting on the object are balanced (ie, zero net force is exerted on the object). Forces are often separated into their components in two orthogonal directions (eg, x-axis forces Fx and y-axis forces Fy) or three directions if considering three-dimensional space. Therefore, equilibrium occurs when these forces sum to zero: ∑Fy=0 ∑Fx=0 There are two forms of mechanical equilibrium. Static equilibrium occurs when the object has zero velocity, and dynamic equilibrium occurs when the object has a constant nonzero velocity. In this question, the vertical forces acting on the vehicle (y-direction) are the weight FW of the vehicle and the force from the ground Fg acting on the tires. Fg is spread over four tires, so each tire experiences approximately Fg4�g4 : ∑Fy=Fg4+Fg4+Fg4+Fg4−FW=Fg−FW=0∑ Similarly, the horizontal forces (x-direction) are the tension T on the steel tow cable and the friction force Ff on the car: ∑Fx=T−Ff=0 Solving the above equation for T gives: T=Ff Therefore, T depends only on Ff when the vehicle is being pulled at a constant velocity (Number I). (Number II) The car's mass does affect the friction force on the car, and therefore the cable tension. However, the friction force also depends on the coefficient of friction and cannot be calculated only from the car's mass. (Number III) The car's velocity does not affect the cable tension. The cable tension equals the friction force on the car, which depends only on the car's normal force and the coefficient of friction. Educational objective:Dynamic equilibrium occurs when all external forces acting on an object sum to zero and the object moves with constant velocity. When pulling a vehicle at constant velocity, the magnitude of the pulling force equals the friction force on the car but acts in the opposite direction.

Which of the following changes will increase the rate at which a mammalian organism loses body heat to the environment? A.Vasoconstriction of the organism's superficial blood vessels B.Vasoconstriction of the organism's pulmonary blood vessels C.Replacement of the organism's lean muscle mass with superficial fat D.Increase in the organism's rate of pulmonary ventilation

Increase in the organism's rate of pulmonary ventilation Heat transfer is the transmission of thermal energy between two objects or systems by processes such as conduction and convection. In conduction, thermal energy passes between two objects (or domains) through physical contact. During convection, the movement of a fluid, such as blood or air, serves to transport heat from warmer regions to cooler regions. Heat transfer between two objects or regions occurs until the temperature equalizes. The physical dimensions of the transfer interface influence the rate of heat transfer (H) between objects. For example, the rate of heat transfer between two objects connected by a thermal conductor depends on the conductor length (L), conductor area (A), and difference between the temperature of the hotter object (TH) and the temperature of the cooler object (TC): H∝A(TH−TC)L�∝���-��� In biological contexts, heat transfer to the environment is facilitated by processes like ventilation (ie, inhalation and exhalation) and the flow of blood through superficial anatomical structures. The regulation of superficial blood flow via vasoconstriction and vasodilation adjusts blood flow to the skin, which is in physical contact with the ambient air. Therefore, changes in skin blood flow modulates conductive heat loss to the environment. Heat transfer to the environment through ventilation occurs through a similar mechanism except that conductive heat transfer to inhaled air is followed by convective heat transfer through exhalation. Therefore, increasing the rate of respiration increases the rate of heat loss to the environment. (Choice A) Vasoconstriction would reduce blood flow to superficial areas and diminish the rate of heat loss to the environment. (Choice B) Vasoconstriction would reduce blood flow to the lungs and diminish the rate of heat loss due to respiration. (Choice C) Replacing lean muscle mass with superficial fat would increase the thickness of the superficial structures that act as thermal insulators, decreasing the rate of heat loss to the environment. Educational objective:Heat transfer from an organism to the environment can be accomplished by increasing superficial blood flow (enha

The researchers want to increase the work done by the subjects during the weight test. Which of the following changes to the test will increase the work by 50%? (Note: Assume the object is lifted straight up off the table.) A.Increasing the mass of the object by 50% and the distance the object is lifted by 50% B.Increasing the mass of the object by 25% and the distance the object is lifted by 25% C.Increasing the mass of the object by 25% and the distance the object is lifted by 20% D.Increasing the mass of the object by 100%

Increasing the mass of the object by 25% and the distance the object is lifted by 20% (Choice A) Increasing m by 50% and d by 50% causes the work to increase by 125% to 13.5 J. This is greater than the 50% increase specified by the question. (Choice B) Increasing m by 25% and d by 25% causes the work to increase by 56% to 9.4 J. This is greater than the 50% increase specified by the question. (Choice D) Increasing m by 100% causes the work to increase by 100% to 12 J. This is greater than the 50% increase specified by the question. Educational objective:The work done to lift an object is the product of the object's mass, the gravitational acceleration, and the distance lifted. Changes to any of these parameters cause a proportionate change in the work done.

When ions X and Y are analyzed in a TOF-MS, ion Y took more time to reach the detector. Which ion's path will be observed having the smaller radius of curvature in MS-MS?

Ion X The TOF-MS is used to separate ions by the amount of time taken for the ions to travel a fixed distance. The ions are initially accelerated in a uniform electric field prior to entering the separation chamber. Ions of greater mass m and smaller charge q (ie, a higher m/q ratio) accelerate more slowly and take longer to reach the detector. Because ion Y is observed taking more time to reach the detector, ion Y has a higher m/qratio and ion X has a lower m/q ratio. In MS-MS, the force F exerted by the magnetic field on moving charges is directly proportional to their charge q. Because this force is centripetal (F=mv2r)�=��2�, the ions are separated into paths of different curvature. Consequently: mv2r∝q Rearranging this equation shows that the radius is proportional to the m/q ratio: r∝mq�∝�� Ions with a higher m/q ratio are less affected by the magnetic field and will curve less within the magnetic field (ie, will have a larger radius of curvature). As a result, the ion with a lower m/q ratio, ion X, will be observed having a smaller radius of curvature. (Choice B) Because ion Y has a higher m/q ratio, it is less affected by the magnetic field and its path has a larger radius of curvature. (Choice C) Because ion X and ion Y took different amounts of time to reach the TOF-MS detector, they must have different m/q ratios. Therefore, their paths will not have the same radius of curvature because the radius also depends on the m/q ratio of the ion. (Choice D) Because both ions have a nonzero charge and velocity when they exit the TOF-MS, they will both also follow a curved path in MS-MS. Educational objective: Ions in TOF-MS are separated by their travel time to the detector, which is directly proportional to their m/q ratio. Ions in MS-MS are separated by their radius of curvature, which is directly proportional to their m/q ratio. Therefore, an ion that takes less time to reach the detector in TOF-MS has a smaller m/q ratio and a smaller radius of curvature in MS-MS.

The photoelectric effect refers to the ejection of electrons from a material when the material absorbs electromagnetic radiation of sufficient energy. As the frequency of electromagnetic radiation increases, what happens to the kinetic energy of ejected electrons?

It increases. The photoelectric effect describes the ejection of electrons from a substance due to the absorption of electromagnetic radiation. Although higher-intensity electromagnetic radiation exhibits greater electric field oscillations, some types of electromagnetic radiation do not cause the ejection of electrons in any case, regardless of intensity. This is due to the electric potential energy between positive charges (protons) and negative charges (electrons). For each electron there exists a discrete value of electric potential known as the work function (W), and the magnitude of energy absorbed through electromagnetic radiation must exceed W for the ejection of an electron to occur. The energy of electromagnetic radiation (E) is proportional to its frequency (f) via Planck's constant (h = 6.62 × 10−34 m2∙kg/s), as given by: E=hf�=ℎ� Accordingly, the ejection of an electron from a surface by incident electromagnetic radiation depends on the frequency of incident electromagnetic radiation. Furthermore, the conservation of energy dictates that the energy absorbed by an electron must contribute to either the ejection of the electron (overcoming the work function) or to the kinetic energy of the electron following ejection: hf=12mv2+Wℎ�=12��2+� Consequently, increasing the energy of electromagnetic radiation (ie, frequency) beyond the value of the work function will increase the kinetic energy of ejected electrons. (Choices A and B) Increasing the energy of electromagnetic radiation must increase the kinetic energy of ejected electrons because the work function of each electron is fixed, and the conservation of energy must be maintained. (Choice D) The kinetic energy of ejected electrons must obey the conservation of energy. Absorbed energy from electromagnetic radiation that does not contribute to surpassing the work function is converted to the kinetic energy of ejected electrons. Educational objective: The photoelectric effect describes the ejection of electrons from a substance due to the absorption of electromagnetic radiation with sufficient energy. Because the energy needed to eject an electron is fixed via its work function, increasing the energy of electromagnetic radiation will increase the kinetic energy of ejected electrons.

In the first experiment, which of the following best describes the vertical motion of the golf ball through the water when the drag force, the buoyant force, and weight of the ball sum to zero? A.It accelerates downward. B.It accelerates upward. C.It moves with constant speed downward. D.It moves with constant speed upward.

It moves with constant speed downward. Newton's first law of motion implies that objects with inertia (ie, mass) resist changes in their velocity. Hence, objects at rest remain at rest and objects in motion remain in motion with constant velocity unless a net external force is exerted upon them. In this question, the golf ball entering the tank of water experiences three forces: the upward buoyant force FB due to the displaced water, the upward drag force FD opposing the ball's downward motion, and the ball's downward weight W. As the ball falls in the water, FD increases until the sum of all the forces on the ball (ie, the net force) is zero: Fnet=FB+FD−W=0 When the net force is zero, Newton's first law implies that the golf ball must move at a constant velocity (ie, zero acceleration). Therefore, because the ball was initially dropped downward, it continues to move downward at a constant velocity in the water. (Choices A and B) The golf ball only accelerates when a nonzero net force is exerted upon it. (Choice D) The golf ball cannot move upward at constant velocity because it was initially dropped downward. Educational objective:When zero net force is exerted on an object, the object must be at rest or moving at a constant velocity.

Light from an incandescent lightbulb passes through an ideal linear polarizer. The intensity of the light is 100 lm before passing through the filter, but 50 lm immediately after. Which of the following explains this discrepancy? A.Refraction occurs as light enters the polarizer. B.Light waves with magnetic fields oriented perpendicular to the axis of polarization are absorbed. C.Light waves with electric fields oriented perpendicular to the axis of polarization are absorbed. D.Reflection occurs before light enters the polarizer.

Light waves with electric fields oriented perpendicular to the axis of polarization are absorbed. Polarization refers to the alignment of transverse wave oscillations in a particular orientation within the x,y,z-coordinate system. For example, a transverse wave traveling along the x-axis causes oscillations that may occur exclusively along the y- or z-axis, or at some angle between the y- and z-axes. Polarization is unique to transverse waves because only transverse waves cause oscillations perpendicular to the direction of propagation. Consequently, electromagnetic radiation can be polarized but sound cannot. A waveform is said to be linearly polarized if waveform oscillations take place within only one plane of the coordinate system. By standard convention, the overall orientation of electromagnetic radiation is the same as the orientation of the electric field component. Polarization filters are optical devices that reorient the polarization of electromagnetic radiation so that radiation exiting the filter is polarized in only one orientation. A linear polarization filter, for example, allows for the transmission of electromagnetic radiation oriented parallel to the axis of polarization but inhibits the passage of radiation oriented perpendicular to this axis. Most light sources emit unpolarized light comprising waveforms oriented in all directions. Even for unpolarized light, however, approximately half of the intensity of electromagnetic radiation is polarized along one of two perpendicular axes. Because only electromagnetic radiation with an electric field oriented parallel to the axis of polarization passes through, the total intensity of light will therefore decrease by 50% when nonpolarized light passes through a linear polarization filter. Linearly polarized waveforms are associated with oscillations that occur in a particular orientation of the x,y,z-coordinate system. A linear polarization filter blocks electric fields aligned perpendicular to the axis of polarization (ie, 50% of total intensity).

Astronauts on the Moon decide to turn on a loudspeaker outside their lunar module to broadcast Earth communications during a moonwalk. Will the astronauts hear the sound coming from the speaker while they are outside the lunar module? A.No, because radio waves require a medium and there is no air on the moon B.No, because sound is a mechanical wave requiring a medium and there is no air on the moon C.Yes, because sound waves, like radio waves, can travel through a vacuum D.Yes, if the speaker's power is turned up to a large enough value

No, because sound is a mechanical wave requiring a medium and there is no air on the moon Mechanical waves (eg, sound and water waves) are disturbances that travel through a medium (eg, air or water). For example, sound waves are created by oscillating vibrations of the air that produce compressions and rarefactions (expansion) in the air as they propagate outward. In contrast, electromagnetic waves are perturbations in the electric and magnetic fields created by an oscillating motion of charges. Because electromagnetic fields exist independent of any medium, electromagnetic waves can propagate even when no medium is present (ie, in a vacuum). In this question, the astronauts on the Moon turn on a loudspeaker to hear communications from Earth, which travel by radio (an electromagnetic wave) through the vacuum of space. The loudspeakers are designed to create sound from a vibrating source that disturbs air molecules; however, no air is present on the Moon. Therefore, the astronauts will not hear sound from the speaker because sound is a mechanical wave. (Choice A) Radio waves are electromagnetic waves and can propagate in vacuum, but the speaker would produce sound waves that require a medium. The air required to carry sound waves is not present on the Moon. (Choice C) Unlike radio waves, which can propagate in vacuum, sound waves are mechanical waves and require a medium. (Choice D) Sound waves do not exist in a vacuum, regardless of the power of the speaker. Educational objective:Mechanical waves such as sound exist only in a medium, but electromagnetic waves can propagate, even in a vacuum.

A tennis ball is thrown and bounced off a wall twice. The displacement of the tennis ball over time is shown. Which point on the plot corresponds to the greatest instantaneous velocity?

Point A

A droplet of oil with mass m and charge −q is suspended exactly halfway between two charged plates, as shown in the figure below. The net force on the charged droplet is zero. Which of the following best describes the signs of the charges on each plate? A.Positive charge on the top plate and equal positive charge on the bottom plate B.Positive charge on the top plate and equal negative charge on the bottom plate C.Negative charge on the top plate and equal positive charge on the bottom plate D.Negative charge on the top plate and equal negative charge on the bottom plate

Positive charge on the top plate and equal negative charge on the bottom plate There is downward force from gravity so an upward force and repelling force at the bottom will keep it suspended in the air An electrostatic force FE exists between two electrically charged objects. Opposite charges attract and like charges repel. In addition, an object in a gravitational field experiences a gravitational force Fg (ie, the weight of the object). In this question, the charged droplet is positioned halfway between two plates and always experiences a downward Fg equal to the weight of the droplet. To remain suspended in static equilibrium, the plates must have a combination of charges that produce an upward FE on the droplet such that the net vertical force (ie, in the y-direction) on the droplet is zero: ΣFy=FE−Fg=0 A positively charged top plate will attract the negatively charged droplet upward, and a negatively charged bottom plate will repel the droplet upward. The combined effect of this configuration of charges produces the required net upward electric force on the droplet. Therefore, the top plate has a positive charge and the bottom plate has a negative charge. (Choices A and D) If the charges on both plates have the same sign, the net electrostatic force on the droplet will be zero due to the electric forces opposing each other. Because the force of gravity still acts downward on the droplet, the droplet cannot remain suspended. (Choice C) This charge configuration produces a net downward electric force, which acts along with the downward gravitational force. Therefore, the droplet cannot remain suspended. Educational objective: Opposite electric charges attract and like electric charges repel. The gravitational force is attractive and acts on all objects within a gravitational field.

Power relationship with work

Power P is the rate of work W done per unit time t: P = W/t. The work done to lift an object is equal to its change in gravitational potential energy ΔPE, which is the product of mass m, gravitational acceleration g, and the change in height Δh: ΔPE = mgΔh. /t

What information about the LED circuit is required to calculate which resistance value should be used? A.Source voltage and LED maximum forward current B.Wavelength of light, LED forward voltage, and LED maximum forward current C.Source voltage, LED forward voltage, and LED maximum forward current D.LED forward voltage and LED maximum forward current

Source voltage, LED forward voltage, and LED maximum forward current Ohm's law states that the voltage V across a resistor equals the current I through the resistor multiplied by the resistance R: V=IRV=IR Ohm's law can be rearranged to calculate the resistance as the ratio of V and I: R=VIR=VI Consequently, the value of the resistance depends only on the voltage across the resistor and the current through the resistor. In this question, the resistor and the LED are connected in a series circuit, so the same current flows through each element. Thus, the LED maximum forward current IF is the same as the current through the resistor: I=IF�=�F By conservation of energy, the voltage rise from the voltage source VS is equal to the sum of the voltage drops across the other elements in the circuit, the resistor VR and the LED VF: VS=VR+VF�S=�R+�F Consequently, VR=VS−VF�R=�S-�F and Ohm's law implies that R=VS−VFIFR=�S-�F�F Therefore, the two voltages and the current are needed to calculate the resistance. (Choices A and D) Ohm's law implies that neither the source voltage nor the LED voltage are sufficient by themselves to calculate the voltage across the resistor. (Choice B) The wavelength of the light does not affect the resistor value, and the LED voltage alone is not sufficient to calculate the voltage across the resistor. Educational objective:In a series circuit, the same current flows through each circuit component. Resistance can be calculated as the ratio of voltage to current using Ohm's law.

spherical mirrors

Spherical mirrors are shaped like a section of a sphere's surface, and the degree to which they bend light is determined by the mirror's focal length. The principal axis of a mirror is the line that passes through its center and is perpendicular to its surface. A mirror's focal length is the distance along the principal axis to the focal point, the location where incident rays parallel to the principal axis converge to or diverge from. Concave (converging) mirrors have their reflective surface curved inward, and they converge light rays to form real images in front of the mirror when the distance of the object is greater than the focal length. Convex (diverging) mirrors have their reflective surface curved outward, and they diverge light rays to form virtual images behind the mirror. The radius of curvature R of a spherical mirror is twice the focal length f: R=2fR=2f Of the given options, only mirrors C and D are convex and create virtual images. Because the light rays in mirror D are reflected away at a smaller angle, these rays can be traced back behind the mirror to a more distant focal point than that traced by the light rays in mirror C (Choice C). Because the radius of curvature is twice the focal length, mirror D also has a larger radius of curvature than mirror C. (Choices A and B) Although mirror B has a larger radius of curvature, both mirrors A and B are concave and therefore create real, not virtual, images under these conditions. Educational objective:Concave (converging) mirrors create real images when the object is placed outside the mirror's focal length, whereas convex (diverging) mirrors always create virtual images. For spherical mirrors, the radius of curvature is twice the focal length: f=R2f=R2.

The bomb cell and the calorimetry device used in the experiment are what types of thermodynamic systems? A.Both are closed systems. B.Both are isolated systems. C.The bomb cell is a closed system, and the calorimetry device is an isolated system. D.The bomb cell is an isolated system, and the calorimetry device is a closed system.

The bomb cell is a closed system, and the calorimetry device is an isolated system. In thermodynamics, the "system" is the physically enclosed space being studied that is separated from the rest of the universe, known as the "surroundings." There are three main types of thermodynamic systems, which are characterized by the type of barrier between the system and its surroundings: An open system allows heat and matter to be exchanged with the surroundings. A closed system allows heat but not matter to be exchanged with the surroundings. An isolated system does not allow heat or matter to be exchanged. According to the passage, the bomb cell houses the combustion reaction, and its surroundings include the water in the calorimetry device. Because the temperature of the surrounding water increased during the combustion reaction, heat can be exchanged between the bomb cell and its surroundings. Because the container is enclosed and does not allow for the exchange of matter, the bomb cell is an example of a closed system. The calorimetry device houses the bomb cell and the water it is submerged in, and its surroundings are the surface it rests on and the nearby air. Because the enclosed walls of the device are completely thermally isolated (poor conductors of heat), neither heat nor matter can be exchanged with its surroundings, and the device is an example of an isolated system. (Choice A) The calorimetry device is an isolated system, not a closed system. (Choices B and D) The bomb cell is a closed system, not an isolated system. Educational objective: An open system allows heat and matter to be exchanged with the surroundings. A closed system allows heat but not matter to be exchanged with the surroundings. An isolated system does not allow heat or matter to be exchanged with the surroundings.

Which of the following will occur if a corrective lens is placed in front of an eye that is unable to form a clear image of a nearby object? A.The focal length will shift away from the eye's lens. B.The focal length will shift closer to the eye's lens. C.Spherical aberration will increase. D.Optical power will decrease.

The focal length will shift closer to the eye's lens. focal length will shift away from eye's lens would be for myopia hyperopia: light focuses behind retina fix with converging lens -focal length will shift closer to eye's lens myopia: light focuses in front of retina fix with diverging lens -focal length will shift away from eye's lens The primary optical components of the eye are the cornea and lens, both of which form a biological converging lens that focuses incoming light rays onto the retina, a structure analogous to the film or sensor within a camera. Refractive errors occur when the eye is unable to focus incoming light rays onto the retina, producing unclear images. Refractive errors are caused by a mismatch between the physical dimensions (eg, length) and optical properties of the eye. For example, hyperopia (ie, farsightedness) is a condition that results when the optical power (S) of the eye is insufficient to refract light rays from nearby objects. A hyperopic eye cannot sufficiently refract light rays that approach the eye at an angle (eg, light rays from nearby objects), producing an image of nearby objects that is sharpest at a location behind the retina. Hyperopia is corrected by placing a converging lens in front of the eye, forming an optical system with greater optical power. Consequently, placing a corrective lens in front of the hyperopic eye shifts the focal length towards the eye's lens and light from nearby objects is focused onto the retina. (Choice A) Myopia (ie, nearsightedness) describes a visual condition in which the eye forms an image of distant objects at a focal point in front of the retina. Correcting myopia (not hyperopia) shifts the image away from the lens. (Choice C) Spherical aberration refers to the optical deficiencies of lenses with perfectly spherical surfaces. The surfaces of the cornea or lens are not perfectly spherical, so no spherical aberration occurs. (Choice D) Placing a converging lens in front of the eye increases the optical power of the eye, allowing it to properly focus light rays emitted from or reflected off of nearby objects. Educational objective:Hyperopia describes the refractive error that results in an individual being unable to see

nodes and antinodes

The nodes and antinodes of a standing wave are locations where the wave amplitude is always zero or always maximal, respectively. The number of nodes and antinodes is determined by the frequency of the standing wave. When a wave is restricted to a finite region by boundary conditions, the resulting reflection of waves can create an interference pattern that appears to stand in place, and therefore is known as a standing wave. Standing wave antinodes form at locations of constructive interference and the resultant wave amplitude is maximal. In contrast, the nodes of a standing wave are locations where the superposed waves exhibit destructive interference, and the resultant wave amplitude is always zero. In this question, the air in a pipe open on both ends forms a standing wave. The ends of the pipe are boundaries where the air medium oscillates freely. Hence, this boundary condition requires that antinodes always exist at the ends of the pipe (ie, positions 1 and 5). An alternating pattern of nodes and antinodes exists between the antinodes at the ends of the pipe, with the number of nodes and antinodes determined by the standing wave frequency. At the fundamental (lowest) frequency, there are two antinodes and one node. At twice the fundamental frequency, there are three antinodes and two nodes. Therefore, the nodes exist at only positions 2 and 4 in the figure.

A speaker and frequency generator are used to create resonances in two pipes. Pipe A of length L is open at both ends. Pipe B is also of length L but is closed at one end. Which statement about the fundamental frequencies produced by the pipes is true? A.The fundamental frequency of pipe A will be twice as great as the fundamental frequency of B, because antinodes must occur at open ends and nodes must occur at closed ends. B.The fundamental frequency of pipe A will be half as great as the fundamental frequency of B, because antinodes must occur at open ends and nodes must occur at closed ends. C.The fundamental frequencies of the pipes are the same, because the speed of sound is the same in both pipes. D.The fundamental frequencies of the pipes are the same, because all pipes of equal length will resonate at the same frequency.

The fundamental frequency of pipe A will be twice as great as the fundamental frequency of B, because antinodes must occur at open ends and nodes must occur at closed ends. Standing sound waves are generated in pipes due to interference between incident waves and reflected waves, which move in opposite directions in the air tube. The resonating sound waves in a pipe create nodes (points of zero amplitude) at closed ends due to restricted air movement, whereas at open ends the sound waves create antinodes (points of maximal amplitude) due to the free motion of air molecules. A pipe open on both ends will resonate when antinodes are formed at each end. A pipe with one end open will resonate when a node is formed at the closed end and an antinode is formed at the open end. In this question, there are two pipes of equal length L; pipe A is open (o) at both ends and pipe B is closed (c) at one end Therefore, pipe A's fundamental frequency will be twice as great as the fundamental frequency of pipe B.

Researchers collide a 1,000 kg car into a stationary concrete barrier with a mass of 100,000 kg. Which of the following statements best explains why the barrier remains stationary when it is struck by the car? A.The coefficient of static friction for the barrier is greater than the coefficient of kinetic friction for the car. B.The kinetic energy of the car is greater than the kinetic energy of the barrier. C.The normal force the ground exerts on the car is greater than the normal force the ground exerts on the barrier. D.The inertia of the barrier is much greater than the inertia of the car.

The inertia of the barrier is much greater than the inertia of the car. According to Newton's first law of motion, an object in motion stays in motion and an object at rest stays at rest. An object's ability to resist changes in speed depends on its inertia I, which equals its mass m: I=m Furthermore, the force required to move a stationary object must be greater than the maximum static friction force Fs, which is proportional to I because the normal force FN is proportional to m: Fs=μsFN=μsmg Fs∝m I∝Fs In this question, the barrier's inertia is 100 times greater than the car's inertia due to their difference in mass. Hence, the force required to overcome Fs and move the barrier is very large because of the barrier's much larger I. The force of the car on the barrier during the collision is smaller than Fs, and therefore the barrier remains stationary when the car collides into it.

Internal energy

The internal energy of a system is the total energy stored in its molecules and is related to its temperature. Energy cannot be created nor destroyed; it can only transfer from one form to another. From the First law of thermodynamics, the change in internal energy (ΔU) is the sum of the amount of heat (Q) transferred to the system and the work (W) done to the system by the surroundings: ΔU=Q+W In this case, nitrogen gas is considered the system and the compressor is considered the surroundings. No direct heat transfer occurs between the system and the surroundings (Q = 0). Despite this, the temperature of the gas increases because its internal energy increases by the amount of work done by the compressor: ΔU=WΔU=W The work associated with the expansion or contraction of a gas is known as pressure-volume work, which is calculated as the product of the external pressure (P) and the change in volume (ΔV): W=PΔVW=PΔV The work done by the compressor is positive because the compressor adds energy to the gas by compressing it from a volume of 3 L to 1 L (ΔV = 2L) at a pressure of 400 Pa. The unit for W is the J, which is equal to 1 Pa∙m3. Hence, 2 L must be converted to cubic meters (m3): ΔV=2 L⋅1 m3103 L=0.002 m3Δ�=2 L⋅1 m3103 L=0.002 m3 Consequently, the work done on this gas is: W=(400 Pa)⋅(0.002 m3)W=400 Pa⋅0.002 m3 W=0.8 JW=0.8 J Therefore, the internal energy of the gas increases by 0.8 J as the nitrogen gas is compressed from a volume of 3L to a volume of 1 L (Choice A). Educational objective:The internal energy of a system increases when heat is transferred to the system and when work is done on the system (ΔU = Q + W). For a system of gases, the amount of work done is equal to the product of the external pressure and change in volume (W = PΔV).

Mean Arterial Pressure (MAP)

The mean arterial pressure (MAP) is used to approximate the average blood pressure of an individual's arteries: MAP = DP + (SP - DP)/3

Thin-film interference is observed when polychromatic light is incident on an interface formed when one semitransparent medium is layered on top of a second semitransparent medium. Which of the following best explains why thin-film interference generates a multicolored array when two semitransparent fluids are used? A.The density of the top fluid varies along the fluid interface. B.The thickness of the top fluid varies along the fluid interface. C.The osmolarity of the top fluid varies along the fluid interface. D.The two semitransparent fluids decrease the number of reflection events at the fluid interface.

The thickness of the top fluid varies along the fluid interface. Thin-film interference refers to the multicolored arrays generated by the reflection events that occur within a system composed of two layers of semitransparent media. The relative intensity of the colors seen within the multicolored array depends on the constructive and destructive interference among waveforms of polychromatic (variable wavelength) light. Interference that occurs within a thin-film system results from differences in the travel path of the light. Some light that is incident on the two-media system will reflect off the surface of the first medium (thin film), and some light will transmit through the first medium before reflecting off the media interface. When light reflected off the surface of the first medium constructively interferes with light reflected off the media interface, an observer perceives bright light. Conversely, when light reflects off the surface of the first medium and destructively interferes with light reflected off the media interface, an observer perceives darkness. Thin-film interference is influenced by the thickness of the film because light waves of a specific wavelength (ie, color) that interfere constructively or destructively at one film thickness may no longer interfere in the same fashion at a different thickness. Therefore, surface tension and other effects that locally distort the surface of a fluid may also cause multicolored arrays to appear on the surface as light that emerges from adjacent segments of the thin film varies in color composition. (Choices A and C) Variations in fluid density and osmolarity cannot explain changes to the interference pattern of light that are necessary to produce multicolored arrays. Furthermore, the fluid density and osmolarity of each medium would not be expected to vary within the same two-media system. (Choice D) Layering two semitransparent fluids increases the number of reflection events, enabling the waveform interference that generates multicolored arrays. Educational objective:Thin-film interference describes the multicolored array generated when polychromatic light is incident on an interface formed by two semitransparent media. Localized discrepa

Removing a resistor from parallel branch A student pulls a plastic comb through her hair on a dry day. Afterward, her hair is attracted to the comb. Which of the following occurs when the comb passes through the hair? During the beta decay process, a neutron transforms into an electron and a proton, and the electron is ejected out of the atom. A closed system containing a number of atoms is electrically neutral and undergoes 120 beta decay processes. What is the resulting net charge of the closed system? (Note: the elementary charge e = 1.6 × 10−19 C)

The total resistance increases when a resistor is removed from a parallel branch. Ohm's law can be used to find current, given resistance and voltage. The equivalent resistance decreases if a resistor is added in parallel. Conversely, the equivalent resistance increases if a resistor in parallel is removed. For resistors connected in parallel, the voltage drop across each resistor is the same and the equivalent resistance increases if a resistor is removed. The current through each resistor in parallel is independent of the others, and the sum of each component current equals the total current. The comb gains electrons and the hair becomes positively charged. The law of conservation of charge states that electric charge is neither created nor destroyed. A neutral object has an equal amount of positive and negative charge. When two objects are rubbed together, electrons can transfer from one object to another. Objects that gain electrons will have an excess negative charge (ie, become negatively charged), and objects that lose electrons will have an equal amount of excess positive charge (ie, become positively charged). The total charge of the system remains constant, but the distribution of charge among the objects in the system is different. In this question, the comb and hair are initially neutral. However, after the comb passes through the hair, the hair and comb are oppositely charged because they attract each other. Therefore, negatively charged electrons are transferred from the hair to the comb, making the comb negatively charged and the hair positively charged, consistent with conservation of charge. 0 According to the law of conservation of electric charge, electric charge cannot be created or destroyed; the total charge is conserved in any process. Moreover, only heat—not matter—can be exchanged with the surroundings in a closed system. Therefore, in a closed system, the total charge must remain constant. In this question, a radioactive nucleus undergoes 120 beta decay processes, where a neutral neutron transforms into one electron and one proton. Consequently, each beta decay process produces the same positive and negative charges. In addition, the system is closed and neutral before the beta decay processes. Due to the conservation of charge and the closed system, the charge balance is maintained. The system will always be neutral regardless of the number of beta decay processes the atom undergoes within the system. Therefore, the net charge of the closed system is zero.

How will the work done by the Lorentz force on an electron traveling through the magnetic field of an MRI scanner change if the magnetic field strength is increased? A.The work will not change, because it is always zero. B.The work will increase, because the velocity of the electron will increase. C.The work will increase, because the force on the electron will increase. D.The work will decrease, because the velocity of the electron will decrease.

The work will not change, because it is always zero. The Lorentz force F acts on a charge q moving in a magnetic field B with velocity v. The direction of F is perpendicular to both the direction of v and the direction of B. The magnitude of F equals the product of q, v, B, and the sine of the angle θB between the directions of v and B: F=qvB sin θB�=qvB sin �B The work W done by F on an object equals the product of F, the magnitude of the object's displacement d, and the cosine of the angle θ between the directions of d and F: W=Fd cos θ�=Fd cos � In this question, the value of B increases, which causes F to increase. However, the value of θ is always 90° because d is the same direction as v, and F is always perpendicular to v. Therefore, W must always equal 0 J because cos 90° is always equal to 0. (Choices B and D) Increasing the magnetic field strength does not change the velocity of the electron. (Choice C) Increasing the magnetic field strength will increase the force on the electron, but zero work is done by the force because the force is perpendicular to the displacement of the electron. Educational objective: The work done by a constant force acting on an object equals the product of the force, the displacement of the object, and the cosine of the angle between the directions of the force and displacement. A force applied perpendicular to the direction of the displacement does zero work on the object.

The spherical aberration of a converging lens can be corrected by reducing the thickness of the lens periphery. The spherical aberration of the lens is caused because light rays emerging from the lens: A.are insufficiently refracted at the lens periphery. B.converge at the lens focal point uniformly. C.are excessively refracted at the lens periphery. D.are scattered due to chromatic dispersion.

are excessively refracted at the lens periphery. An ideal lens generates an image of an object at a single focal point, regardless of the locations at which the light rays enter and exit the lens. Spherical aberration describes the phenomenon by which real lenses' perfectly rounded (ie, spherical) surfaces do not produce an image at a single point, but rather at a series of focal points. In converging lenses, the location of each focal point is related to the distance from the principal axis (ie, the lens center) at which light enters and exits the lens. Spherical aberration is most pronounced among rays entering and exiting the lens periphery (ie, distant from the principal axis). Furthermore, correcting spherical aberration in converging lenses requires using an aspherical lens in which the thickness of the lens periphery is decreased relative to a perfectly rounded lens. Because reducing the thickness of the lens periphery will lead to less refraction of light, light rays exiting the periphery of a spherical converging lens can be said to refract excessively, converging on a focal point that is too close to the lens. (Choice A) Spherical aberration in a converging lens is characterized by refractive events that focus light emerging at the lens periphery more dramatically than light emerging closer to the lens center. Therefore, light is excessively, not insufficiently, refracted at the lens periphery. (Choice B) All lens and mirror aberrations describe a failure of optical instruments to converge or diverge light rays uniformly. (Choice D) Chromatic dispersion describes the failure of a lens to focus multicolored light onto a single point. Chromatic dispersion in converging lenses is corrected by using a diverging lens to increase the thickness of the lens periphery. Educational objective:Spherical aberration occurs when lenses with perfectly rounded surfaces focus light at multiple focal points. Spherical aberration is most pronounced among light rays entering and exiting the periphery of converging lenses.

The absolute temperature of ideal gas molecules stored in a container is directly proportional to the: A.quantity of gas molecules. B.intermolecular forces between gas molecules. C.average kinetic energy of gas molecules. D.maximum velocity of gas molecules.

average kinetic energy of gas molecules. In common terms, temperature (T) is an objective measure of the relative "heat" or "cold" contained with an object or system. Temperature influences important physical properties like the physical state and reactivity of matter. The absolute temperature scale is used to quantify the temperature of objects relative to absolute zero, the temperature at which matter achieves the lowest possible quantity of total energy (kinetic energy + potential energy). Absolute zero is considered "absolute" because it is the same for all matter, regardless of atomic structure or molecular configuration. The unit of absolute temperature is the Kelvin (K), and the gradations of the absolute temperature scale are equal in size to those of the centigrade scale. The scales differ only in the placement of the zero value. Consequently, the temperature in Kelvin (TK) relates to the temperature in Celsius (TC) through the following expression: TK=TC+273.15�K=�C+273.15 Fundamentally, kinetic energy is the key determinant of absolute temperature. Because temperature is typically sampled from multiple atoms or molecules, however, the temperature of matter reflects the average kinetic energy (KE) of a collection of atoms or molecules: T∝ ∑KE of each moleculeQuantity of molecules�∝ ∑KE of each moleculeQuantity of molecules Therefore, the temperature of gas molecules moving throughout an enclosed container is determined not by the kinetic energy of any one gas molecule but rather by the average kinetic energy of all gas molecules. (Choice A) The quantity of gas molecules is directly proportional to the pressure and volume, but not the temperature, of a gas. (Choice B) Although significant intermolecular forces between gas molecules would influence the kinetic energy of those molecules, intermolecular forces are not observed between ideal gas molecules. (Choice D) Gases exhibit a range of possible kinetic energy values at all temperatures. However, temperature is not related to the kinetic energy of individual molecules at extreme kinetic energy values, but rather the average kinetic energy of all molecules. Educational objective:The absolute temperature scale quantifies temperat

An astronaut drifts through space along the surface of her spaceship. She is perpendicular to the spaceship with her feet toward it. The astronaut moves as a rigid body with constant velocity and no rotation. Which of the following occurs when the astronaut momentarily strikes a protruding portion of the spaceship with her foot? The astronaut: A.slows down and continues along her original path with no rotation. B.turns upside down and slowly falls to the ship's surface. C.continues along her original path while spinning about her center of mass. D.stops, spins about the protrusion, and falls to the ship.

continues along her original path while spinning about her center of mass. A torque is a rotational force that makes an object spin about a pivot point. A pivot point can be a fixed point such as a hinge or axle seen in mechanical systems. For an unrestrained object like an astronaut floating in space, the pivot point is the center of mass CM. Torque is generated by a force F applied perpendicularly to a lever arm (ie, the structure connected to the pivot point): T=r⋅Fsin(θ)�=r⋅Fsinθ where θ is the angle between the lever arm and the force, and r is the length of the lever arm. Upon striking the protrusion of the ship, the astronaut's foot experiences an impact force due to the collision. The foot, leg, and torso act as the lever arm between the impact force and the astronaut's center of mass. Therefore, the collision generates a torque about the astronaut's CM, making the astronaut spin. The astronaut's translational (ie, non-rotational) motion does not change significantly because gravitational forces are negated in microgravity. However, the astronaut continues along her original path with reduced velocity because a portion of the impact force acts perpendicular to her original path, causing negative acceleration.

When the angle of inclination of the ramp increases, kinetic friction: A.decreases because the weight component perpendicular to the ramp decreases. B.decreases because the weight component parallel to the ramp decreases. C.increases because the weight component perpendicular to the ramp increases. D.increases because the weight component parallel to the ramp increases.

decreases because the weight component perpendicular to the ramp decreases. Kinetic friction Fk is the frictional force between two objects sliding against each other, and it is the product of the coefficient of kinetic friction μk (specific to the two surfaces) and the normal force N (the perpendicular force one surface exerts on another): Fk = μkN When the mass slides down a ramp with angle of inclination θ, its weight W can be split into two component force vectors, the sum of which is the weight vector. One component of the weight is parallel to the ramp's surface (W sin θ) and points down the ramp, causing the mass to slide. The other component is perpendicular to the ramp's surface (W cos θ) and keeps the mass in contact with the ramp. The normal force is equal and opposite to this perpendicular component: N=Wcosθ Substituting this expression into the above equation for kinetic friction gives: Fk=μkWcosθ As θ increases, the value of cosine decreases, and both the perpendicular component of the weight and the normal force also decrease. Therefore, because kinetic friction is proportional to the normal force, kinetic friction must decrease.

Compared to other diffraction techniques, the advantage of x-ray diffraction is that it enables: A.determination of three-dimensional molecular structure. B.determination of the work function corresponding to each electron. C.measuring the wavelength of electromagnetic radiation. D.measuring the linear polarization of light.

determination of three-dimensional molecular structure. Not all forms of electromagnetic radiation undergo diffraction when incident upon one or more slits. For example, x-rays are a form of electromagnetic radiation that cannot undergo classic slit diffraction because the wavelengths of x-rays range from 1 × 10−11 m to 10 × 10−11 m, which is always exceeded by the lengths of industrially fabricated slits. However, the wavelength of some x-rays is comparable to the typical distance between atoms within the molecular structure of most materials. Consequently, exposing a sample of a purified and crystallized material to x-ray radiation may produce a diffraction pattern unique to that particular substance. X-rays diffract within molecules because the space between atoms is comparable to the wavelength of x-rays. X-ray diffraction through a sample of a purified and crystallized material can be used to determine its three-dimensional molecular structure and packing.

Ultrasonic shock wave devices may be used in medical settings to disrupt disease structures located deep in the body. Among other variables, the device user can control the frequency of emitted waveforms. The adjustment of waveform frequency: A.can be used to provide direct auditory feedback to the user. B.enables high-amplitude resonance within diverse target tissues. C.may eliminate the attenuation effects associated with tissue interfaces. D.assists in the measurement of bodily fluid velocity.

enables high-amplitude resonance within diverse target tissues. Ultrasonic sound waves (ie, ultrasound) are mechanical waves that propagate at a frequency above the upper bound of the human auditory spectrum (~20 kHz). Ultrasonic sound waves behave much like audible sound waves that can be detected by the human ear. However, the relatively small wavelength of ultrasonic waves allows them to propagate through body tissues without diffracting significantly. Propagation without diffraction enables the use of ultrasound waves in medical imaging contexts. Unlike ultrasound techniques used for medical imaging, shock wave ultrasound is a non-imaging treatment modality in which the mechanical energy of ultrasonic sound waves is transmitted to structures associated with human disease. Shock wave absorption by these tissues causes high-amplitude vibrations that contribute to tissue destruction. Although standing wave vibrations may take place in any object following perturbation, vibrations that occur in non-acoustic objects are generally inaudible because the amplitude (A) of the vibrations is too small or because the resonance frequency (f0) falls outside the audible range. The high-amplitude vibrations associated with shock wave ultrasound, for example, occur only because the shock wave frequency (f) approaches (or is equal to) the resonance frequency of the target structure. The resonance frequency of disease structures may change in accordance with size and material composition. Shock wave therapy devices must therefore allow the user to adjust the frequency of the emitted shock waves to ensure effectiveness in destroying particular tissue types. (Choice A) Shock wave ultrasound utilizes ultrasonic waves that transmit at frequencies beyond the human auditory spectrum, making direct auditory feedback from the device to the user impossible. (Choice C) Regardless of frequency, all sound waves attenuate (ie, lose intensity) somewhat when propagating through a medium. Furthermore, attenuation may occur as sound waves pass between media. (Choice D) Doppler ultrasound is a specialized imaging technique that allows for the characterization of dynamic structures. However, shock wave ultrasound is typically used to de

The laser Doppler sensor is positioned at the top of the ramp and emits light at 500 nm toward a block sliding down the ramp. The sensor records the data shown in Figure 2. During the interval from 0.3 s to 0.7 s, the wavelength of the light reflected back to the sensor is: A.greater than the emitted light by a constant value. B.less than the emitted light by a constant value. C.continuously increasing with time. D.continuously decreasing with time.

greater than the emitted light by a constant value. The Doppler effect occurs when a periodic signal emitted from a source (eg, sound, light) is perceived by an observer to have a different wavelength λ due to the relative motion between the source and the observer. The magnitude of this change in λ is proportional to the relative speed v between the source and observer: Δλ∝v If the source is moving toward the observer, the perceived λ of the signal decreases because the source is closer to the observer for each subsequent peak in the wave, and thus the waveform is compressed. If the source is moving away from the observer, λ increases because the source is farther away for each subsequent peak in the wave, and thus the waveform is stretched. In this question, the laser Doppler sensor transmits light toward the block and records the reflected signal to determine its speed. Because the reflected signal is recorded by the sensor, the block acts as the source and the sensor acts as the observer. The speed of the block in Figure 2 during the interval from 0.3 s to 0.7 s is a constant 0.5 m/s. Therefore, the Doppler shift in the observed λ will be constant over time. Moreover, because the block is moving away from the sensor, the λ of the light recorded by the sensor will be greater than the λ of the light originally emitted by the sensor.

The advantage of using gamma rays for tumor therapy over x-rays is that gamma rays: A.are not electromagnetic radiation. B.are photons. C.have higher energy. D.have a longer wavelengt

have higher energy. Electromagnetic radiation includes different types of wave phenomena, such as radio waves, visible light, x-rays, and gamma rays. These different categories of waves are often organized into the electromagnetic spectrum, ordered by decreasing wavelength λ and increasing frequency f. The energy E of electromagnetic radiation equals the product of Planck's constant h and f: E=hf Hence, E is directly proportional to f. In this question, f of the gamma rays described in the passage is 50 × 1018 Hz, and f of the x-rays is 100 × 1015 Hz. Because f is higher for gamma rays than x-rays, E will also be higher for gamma rays than for x-rays. Therefore, the gamma rays used for tumor therapy have a higher E than the x-rays used for imaging. (Choices A and B) Both x-rays and gamma rays are electromagnetic radiation composed of photons. (Choice D) The wavelength of gamma rays is shorter than the wavelength of x-rays, not longer. Educational objective:The electromagnetic spectrum consists of different types of radiation ordered by wavelength, frequency, or energy. Electromagnetic radiation with a shorter wavelength has higher frequency and energy.

The cardiac output of a subject is directly proportional to their: A.heart rate. B.vascular resistance. C.left ventricle volume. D.total blood volume.

heart rate. The cardiac output CO is the amount of blood pumped out of the left ventricle in 1 minute. CO is defined as the product of the stroke volume SV of the heart and the heart rate HR: CO=SV⋅HR The SV is the volume of blood pumped out in a single heartbeat. The SV depends on the change in the volume of the left ventricle before and after the contraction of the heart. The volume of the left ventricle before contraction is the end diastolic volume EDV and the volume after contraction is the end systolic volume ESV, yielding: SV=EDV−ESV In this question, HR is the only answer choice that is included in the equation for CO. Based on this equation, CO is directly proportional to HR because any changes in HR will lead to an equivalent change in CO. (Choice B) CO can be calculated based on the vascular resistance. However, CO and resistance are inversely proportional, not directly proportional. (Choice C) The volume of the left ventricle is not a constant value and can influence CO in different ways. Increasing the EDV could increase the SV and CO, but a greater ESV will decrease the SV and CO. (Choice D) The total blood volume does not influence CO. Educational objective:The cardiac output is the volume of blood the heart pumps in 1 minute. It is calculated by multiplying the stroke volume of the heart and the heart rate.

For equally sized trocar-cannula systems, incisions made for blunt-tipped trocars are smaller than those made by sharp-tipped trocars, forcing the skin to stretch more around the cannula. This option better prevents slipping after the cannula is inserted because: A.it decreases the contact surface area. B.it decreases the static friction. C.it increases the normal force. D.it increases the coefficient of static friction.

it increases the normal force. Static friction is the frictional force that prevents two surfaces from sliding. After the cannula is inserted, static friction between the cannula and skin prevents slipping because static friction counters the forces that promote sliding. Static friction has an upper limit and if the forces that promote sliding exceed this value, slipping occurs. The upper limit of static friction Fs is the product of the coefficient of static friction μs and the normal force N (the perpendicular force one surface exerts on the other): Fs = μsN The greater the upper limit of static friction, the better the cannula is prevented from slipping. Therefore, slipping can be better prevented by increasing the normal force. The normal force keeping the cannula in place is due to the skin pressing on the cannula. According to the question, cannulas inserted with blunt-tipped trocars experience greater stretching of the skin. Therefore, the cannula is subject to a greater normal force, producing a greater static friction force. (Choice A) According to the question, the cannulas are of equal size, and therefore the sizes of the contact areas are the same. (Choice B) Decreasing the static friction is more likely to cause the cannula to slip. (Choice D) The coefficient of static friction depends only on the properties of the surfaces involved. Since both situations involve the same two surfaces (cannula and skin), the coefficient of static friction is the same.

The refractive indices of the glass optical fiber, polymer lens, and liquid crystal lens described in the passage are denoted as n1, n2, and n3, respectively. The refractive indices of the glass optical fiber and the two focusing lenses are related by which of the following?

n1 > n2 and n1 < n3 Going from a high n to low n the angle of refraction will get larger-bends away from normal Going from a low n to high n the angle of refraction will get smaller- bends towards normal more Snell's law governs the refraction of light when crossing a boundary of two media with different refractive indices. Light traveling from a medium with a higher refractive index into one with a lower refractive index will have a refracted angle that is greater than the incident angle.

An underwater diver is able to shine a laser onto the underwater portion of a distant boat. However, the diver is unable to shine the laser onto the portion of the boat that is above the surface. Which of the following best explains this phenomenon? A.Diffraction B.Dispersion C.Polarization D.Reflection

reflection Water and air have different indices of refraction n, which indicate the relative speed of light in each medium. A medium's n increases with density; n of water (n = 1.3) is greater than that of air (n = 1). Refraction, the bending of light, occurs at the boundary between two different mediums with different values of n. If light passes from a high to low n, such as from water to air, light bends away from the normal (axis perpendicular to the surface) and toward the surface. As the incident angle (angle between incident ray and the normal) increases, the light ray is refracted closer to the surface. At a "critical angle", light is refracted at a 90° angle and continues parallel to the surface. At incident angles greater than the critical angle, light reflects back into the water, causing total internal reflection. When the diver shines the laser towards a distant boat, the incident angle likely exceeds the critical angle. Therefore, the reflection of light best explains why the laser beam bends back into the water and doesn't reach the portion of the boat above the surface. (Choice A) Diffraction is the bending of light around physical corners or very narrow gaps. Significant diffraction would not occur at the water-air surface. (Choice B) Dispersion is the spreading of light into its different frequencies (colors) due to differences in the index of refraction for different frequencies of light. The effects of dispersion would not significantly change the direction of the laser beam. (Choice C) Polarization aligns transverse electromagnetic radiation along a specific orientation, such as vertical, horizontal, etc. Light can be polarized during reflection, but polarization does not cause reflection. Educational objective:Because the refractive index of water is greater than that of air, light traveling from water to air will refract toward the surface of the water. At a critical angle, light is refracted at 90° and is parallel to the surface. Above this angle, all of the light will be reflected away from the surface (total internal reflection).

The locations of the bright and dark bands produced by light passing through a single slit depends on the: initial light intensity. slit width. wavelength.

slit width and wavelength Diffraction is broadly defined as the bending of light around edges or objects. Classic slit diffraction occurs as a uniform wavefront of monochromatic light arrives at a slit (ie, confined gap) in which the width of the slit (a) is comparable to the wavelength of the light (λ), resulting in the dispersed propagation of light away from the center of the slit. Diffraction through a single slit produces a pattern of dark and bright bands on a flat background surface distant to the slit. Bands occur when the bending of light causes the distance (path length) traveled by some waves to be longer than that of others. When the path lengths of two light waves differ by λ/2, the waves arrive at the background out-of-phase (ie, the peak of one waveform coincides to a trough of the other). As a result, destructive interference occurs such that dark bands in the diffraction pattern are produced. Conversely, light bands result from zero or minimal destructive interference. Dark bands (minimum light intensity) due to destructive interference occur when diffracted light waves pass through the slit at angles (θ) that are a function of the slit width and an integer multiple (m = ±1, ±2, ±3...) of the wavelength: According to this relationship, decreased slit width or increased wavelength tends to widen the band pattern such that greater distances are present between light and dark bands. Conversely, increased slit width or decreased wavelength will reduce the distance between the light and dark bands. Therefore, both slit width and wavelength influence the angle of propagation associated with the dark and light bands in the pattern of diffracted light (Numbers II and III). (Number I) The initial intensity of the light affects the intensity of the diffracted light, but does not influence the location of the bright and dark bands in the diffraction pattern. Educational objective:Single-slit diffraction is an optical phenomenon that demonstrates the waveform nature of light. The location of the bright and dark bands associated with a given diffraction event is related to slit width and the wavelength of light.