UWorld Physics
velocity of sound wave depend on
1. higher temp, higher velocity 2. Velocity is slowest in gases, faster in liquids, and fastest in solids. 3. Within a phase of matter, velocity increases with stiffness and decreases with density
state function
A function that depends only on the initial and final states of a system, not on the path in between. - Mass, pressure, density, energy, temperature, volume, enthalpy, entropy, Gibbs free energy and chemical composition
An object is launched with a one-time burst of propulsion away from the surface of a planet with no atmosphere. Which of the following best describes the changes that occur as the object moves away from the planet'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.
After the object (eg, a rocket) is launched from a central body, the only force present in the system is gravity. As the rocket moves away, the gravitational force is oriented toward the central mass. Therefore, work done by gravity progressively decreases the velocity and the kinetic energy of the object. At the same time, potential energy increases as the radial distance increases. But conservation of energy is maintained correct answer is C
A spring is extended 15 cm from its equilibrium point. If the spring constant k is 75 N/m, the magnitude and direction of the elastic force Fel are described by which of the following? A.1.1 × 10^1 N; oriented away from the equilibrium point B.1.1 × 10^1 N; oriented toward the equilibrium point C.1.1 × 10^3 N; oriented away from the equilibrium point D.1.1 × 10^3 N; oriented toward the equilibrium point
Elastic Force (Fel) =−kx - elastic force is expressed as negative quantity, because the force acts counter to the direction of the displacement and bring the spring back to its equilibrium position - Fel points toward the equilibrium point because Fel acts to oppose the extension and restore the stretched spring back to its shorter natural position. The correct answer is B
Different substances have different thermal conductivities k, which measure how well heat is transferred by molecular collisions. The heat flow rate per unit area H is defined by: H=k*ΔT/L where ΔT is the difference in temperature over a distance L. The tiled part of a floor in a room feels colder than the carpeted part because: 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.
For a person straddling the tile and carpet, the temperature gradient between the body and each object is the same because the carpet and the tile are at the same (room) temperature. 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. -> carpet is more like a thermal insulator Thermal conductivity k measures how well a material transfers heat at a specified temperature gradient. correct answer is B
A large number of monoatomic ideal gas molecules are stored within a closed container at a temperature of 200 K. What is the average translational kinetic energy of the individual gas molecules? (Note: Use Boltzmann's constant k = 1.381 × 10−23 J/K.) A.2.8 × 10−23 J B.4.2 × 10−23 J C.2.8 × 10−21 J D.4.2 × 10−21 J
KE = 3/2*k*T = 3/2* (1.381*10^-23)*200 = 4.2*10^-21 The kinetic molecular model describes macroscopic characteristics of gases that are related to the constant motion of freely moving gas molecules. this KE equation is typically used in calculating single gas molecule correct answer is D
what is wavelength equation if pipe open at both ends
L = λ/2
what is wavelength equation if pipe close on one end
L = λ/4
A 1-m spring is compressed to half its original length. What is the potential energy stored within the spring? (Note: k = 40 N/m) A.2.5 J B.5.0 J C.10 J D.20 J
Potential energy refers to a form of stored energy that depends on the spatial position or configuration of objects stretching or compressing a spring away from its equilibrium point (ie, its position at rest) increases its elastic potential energy (Uel) because displacing a spring requires doing work against the elastic forces resisting displacement elastic potential energy (U) = 1/2*K*X^2 U=1/2*40*(0.5)^2 = 5 correct answer is B
The compressor exerts a pressure of 400 Pa to compress nitrogen gas from 3 L to 1 L. If no heat transfer occurs, how much will the internal energy of the gas change? (Note: 1 m3 = 1000 L.) A.0.8 J B.1.2 J C.800 J D.1200 J
SI unit of pressure is Pa; not atm SI unit of volume is m^3 U (internal energy) = W + Q there is no heat transfer, so Q=0 => U = W = P*V 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 P = 400 Pa, dV = 2L = 2* 10^-3 work = 400 Pa * (2*10^-3) m^3 = 0.8 J correct answer is A
That the spherical aberration of a converging lens is corrected by reducing the thickness of the lens periphery means that the light rays emerging from aberrant converging lenses: 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
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. correct answer is C
Which thermodynamic quantity involved in the Hampson-Linde cycle is a state function? A.Entropy of nitrogen, because it describes an equilibrium state of the system B.Entropy of nitrogen, because it describes a path to an equilibrium state of the system C.Work done by the compressor, because it describes an equilibrium state of the system D.Work done by the compressor, because it describes a path to an equilibrium state of the system
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. - system's entropy is a measure of its current state of disorder and does not depend on how the system arrived at that state 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. - work is a process function because it describes what was done to the system to change its state Correct answer is A
An observer perceives a sound to be lower in frequency when the sound source is moving away from the observer. This shift in the frequency of the perceived sound occurs because: A.the sound waveform velocity decreases as the distance between source and observer increases. B.sound waveforms are reflected off environmental objects nearby. C.successive sound waveforms are emitted further away from the observer D.the sound wave intensity decreases as the distance between source and observer increases
The Doppler effect describes apparent changes in the velocity of waveforms that lead to changes in the observed frequency of those waveforms, which are known as Doppler shifts; sound wave itself will not change; the only change is the perceived sound velocity related to the distance of observer -> when the distance between observer and source increases, perceived sound wave velocity decreases choice D is wrong -> reduce in sound wave intensity is unrelated to the motion of the source and observer correct answer is C
A monoatomic ideal gas is sealed within a container featuring a piston fixed in place at one end. How will the heat capacity C of the gas change if the piston is allowed to move freely? A.C will increase, because the gas can expend energy by doing work on the piston. B.C will decrease, because the movement of the piston will prevent heat transfer. C.C will remain constant, because the internal energy of the gas can no longer change. D.C will remain constant, because the gas molecules are monoatomic and ideal
This expression shows that CV is less than CP because some heat energy transferred into a gas stored at constant pressure may be converted to pressure-volume work during the expansion or compression of the gas. correct answer is A
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
Viscosity is a measure of internal friction in a fluid, and the friction arises from interaction between fluid layers dynamic shear force = (viscosity) (V2-V1)/(y2-y1) y: fluid location separated by distance 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. choice B is wrong -> the transition of fluid is horizontal, so gravitational potential energy plays no role choice C is wrong -> convection is transfer of heat d/t large scale of molecule motion.there is no transfer of heat correct answer is D
When sound passes from air to the tympanic membrane, what changes occur to the sound's intensity and velocity? A.Both increase B.Both decrease C.Intensity increases; velocity decreases D.Intensity decreases; velocity increases
When sound crosses from one medium to another, a portion of the wave's energy is reflected. Therefore, sound waves lose energy (are attenuated) and their intensity decreases when passing from air to a solid structure, such as the tympanic membrane correct answer is D
The relationship between the length of a spring and the force required to stretch the spring is shown below. graph is #2 in word doc 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
Work = Force * velocity to find work, calculate the area under the curve. DO NOT calculate the slope (slope = (F2-F1)/(V2-V1)) correct answer is A
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
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. choice B is wrong -> x-ray does not cause electron ejection choice C is wrong -> wavelength can be determined easily with other diffractive technique choice D is wrong -> linear polarization is measured with linear polarization filter correct answer is A
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
bomb cell: combustion reaction happens here and water temperature increases d/t the reaction -> this indicates there is heat exchange withe the surrounding => bomb cell is closed system calorimetry device: the wall is thermally insulated, so no matter or heat is exchanged with the surrounding -> calorimetry device is isolated system correct answer is C
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.
electro magnetic spectrum (from high f to low f): gamma ray > x-ray > ultraviolet > visible > infrared > microwave > radio higher the frequency of the wave, hotter the object. since x-ray has higher f and energy, it will be hotter than infrared correct answer is A
To test the integrity of the capacitor, researchers maintained a voltage of 50 mV across the parallel portion of the circuit for several minutes. During this time, how much energy was stored in the capacitor? (C= 2 microF = 2*10^-6) A.2.5 × 10−9 J B.5.0 × 10−9 J C.5.0 × 10−8 J D.1.0 × 10−7 J
energy = 1/2 *C *V^2 U = 1/2 * (2*10^6) (50*10^-3)^2 = 2.5*10^-9 J correct answer is A
Which of the following expressions gives the magnitude of the work done by the frictional force F if the synthetic skin slides down the entire length L of the ramp and then is pushed back up to its original position? A.0 B.(F)(L) C.(F)(2L) D.(F)(3L)
fiction is a non-conservative force that does not conserve total mechanical energy, and word is depend on the total distance travel though which the force is applied W=F*d = F * 2L choice A is wrong -> if the force is conservative (gravity, electrostatic), W will be 0, but friction is not conservative force, so we calculate total distance travel, not net displacement correct answer is C
A 10-kg block is suspended in air by a single string that passes through a pulley and is attached on the other side to a 35-kg block that is on the verge of sliding on the ground. What is the coefficient of static friction between the larger block and the ground? (Note: The magnitude of the vertical force the small block exerts on the large block is 87 N.) * See word document for picture* A.0.11 B.0.15 C.0.19 D.0.23
horizontal and vertical force applied on large block Fx = 100cos60 = 50N Fy = 100sin60 = 87N F_f,s = 50N = static friction coefficient * Fn = static friction coefficient * (Fg-Fy) static friction coefficient = 50 / (350-87) = 50/263 = 0.19 correct answer is C
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
kinetic friction = kinetic coefficient * normal force Fn = mg*cos0 normal force is perpendicular with the ramp, and as angle increase, normal force decrease correct answer is A
In the experiment, the magnitude of the kinetic frictional force between the ramp and the synthetic skin depends on: I. the area of the contact surface. ll. the mass of the load. lll. the speed of the synthetic skin. A.I only B.II only C.I and III only D.II and III only
kinetic friction force = kinetic coefficient * Fn Fk = kinetic coefficient * m *g so Fk is not depend on the speed of the synthetic skin or surface area correct answer is B
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.
the greater the static friction, greater the stretch, and greater the normal force (skin pressing on the cannula more) static friction = coefficient of static friction * normal force static friction coefficient is depend on the property of the surface involved , and surface does not change -> D is wrong correct answer is C
An object with the same density as water is stationary and suspended in a container filled with water. Ignoring the effects of fluid friction, what will happen to the object after a downward force is momentarily applied? A.The object will sink at a constant velocity. B.The object's downward velocity will increase with time C.The object will quickly stop sinking. D.The object will sink before returning to its initial position
the moment after the downward force is applied, the net force will return to 0, and the object will either remain motionless or move in constant velocity. *the question is asking for the state of object AFTER the force is applied, not the state when the force is applied correct answer is A
The hydrostatic weighing container above is filled with water. If point A is 0.7 m above the bottom of the container, what is the fluid pressure at point A? (Note: The density of water is 1,000 kg/m3.) ** pic is #3 on word doc A.7.0 × 10^3 N/m2 B.1.0 × 10^4 N/m2 C.1.3 × 10^4 N/m2 D.2.0 × 10^4 N/m2
to calculate hydrostatic pressure, use P = fluid density * g * height of the fluid above the point of interest P=1000*10*1.3 = 1.3 * 10^5 correct answer is C
Four charged particles of equal mass are initially fixed in place along a straight line, as shown above. If all the charged particles are released at the same time, which particle would initially accelerate most rapidly? ** #4 is on word doc A.Particle A B.Particle B C.Particle C D.Particle D
use electric force to solve the problem: Fe = kQ1Q2/r^2 particle B experience 3 forces in the same direction: Fab, Fbc, and Fbd, and the sum of these forces give particle B the largest magnitude, so particle B will accelerate the fastest while the particle is released correct answer is B
The blood leaving the aorta reaches the circle of Willis, a collection of arteries that supplies blood to the brain. Assume that it takes 600 ms for blood to reach the circle of Willis and that its average velocity is reduced to 61 cm/s. What is the average acceleration experienced by the blood? * passage info: blood velocity is 101 cm/s at t=0s (before it leaves aorta) A.−67.0 cm/s2 B.−0.670 cm/s2 C.0.670 cm/s2 D.67.0 cm/s21
v1 = 101 cm/s t1 = 0s v2 = 61 cm/s t2 = 600ms a = (v2-v1)/(t2-t1) = -67 cm/s2 correct answer is A (running out of time when working on this problem)