MCAT Physics Error Log (UWorld)

When the angle of inclination of the ramp increases the parallel component of the weight causing the mass to slide ____________ and the kinetic friction____________.

(a) increases (b) decreases Because the sum of the parallel and perpendicular components is constant, the perpendicular component (normal force) decreases. Because kinetic friction is proportional to the normal force, kinetic friction decreases.

cardiac output

(stroke volume) x (heart rate) The volume of blood ejected from the left side of the heart in one minute.

A volunteer with a mass of 80 kg is suspended by his arms on Earth. What is the approximate tension on lumbar disc 5, which is located near the volunteer's center of mass? (Note: The acceleration of gravity is g = 10 m/s2)

*400 N* Tension (T) = mg Lumbar disc 5 is located close to the volunteer's center of mass. Therefore, approximately half the volunteer's body mass is located below lumbar disc 5. As a result, T on lumbar disc 5 is equal to approximately half the volunteer's W: T = Mg/2 = (80 kg)(10 m/s2)/2 = 400 N

An individual that weighs 700 N in the air has an apparent weight of 40 N when submerged in water. What is the volume of the displaced water? ρ(water) = 1 kg/L acceleration due to gravity = 10 m/s2

*66 L* -The FB acting on the individual is the difference between W(air) and W(apparent): FB=W(air)−W(apparent) FB=700 N−40 N=660 NF -Fb=ρVg The volume V displaced by the individual is calculated using the values of ρ(water) and g given in the passage: V=Fb/ρg V=660 N / (1 kg/L)(10 m/s2)=66 L

Hooke's Law Equation

*F = -kx* States that: the force exerted by a spring is equal to the spring constant times the distance the spring is compressed or stretched from its equilibrium position (k) - the spring constant which depends on the stiffness and other properties of the spring (x) - the distance that the spring is stretched from its equilibrium position

Because friction resists sliding, kinetic friction always decelerates sliding objects. Therefore, the acceleration of the load is:

*negative* -the velocity of the object decreases over time

kinetic friction

- occurs when surfaces slide against each other - friction that opposes motion once the motion has already started - Fk = μkN

surface tension of alveolar fluid

-Causes alveoli to assume smallest possible diameter -Accounts for 2/3 of lung elastic recoil -Prevents collapse of alveoli at exhalation

Delta G equation

-change in free energy -ΔG = ΔH - T ΔS

negative ΔH

-exothermic -energy is released as heat -the enthalpy of the products is lower than the enthalpy of the reactants

negative ΔH and positive ΔS

-negative ΔG -always spontaneous

counterclockwise torque

-positive torque -by the right-hand rule counterclockwise corresponds to a torque vector directed out of the page

Ohm's law for flow

-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

Archimedes' Principle

-the buoyant force on an object is equal to the weight of the fluid displaced by the object -Fb = ρVg (ρ = density) (g = gravitational acceleration)

static friction

-the frictional force that prevents two surfaces from sliding -occurs when surfaces do not slide because the magnitude of static friction fully counteracts an applied force

Latent heat of fusion

-the heat needed to change one mole of the substance from a solid to liquid at its melting point -Ex: 1 mole of water from a solid to a liquid at 0*C (MP of water) -It is the energy required to disrupt the ice lattice by breaking some of the hydrogen bonds between the water molecules - Q = mL

power measures

-the rate at which someone or something does work -the amount of work done by a force acting on a system per unit time

atm to mmHg to torr

1 atm = 760 mmHg = 760 torr

1. Deposition 2. Sublimation

1. gas to solid (exothermic) 2. solid to gas (endothermic)

Blood flows through a vessel in the leg at an average velocity of 10 cm/s. How much glucose passes by a segment of the blood vessel each second if the radius of the blood vessel is 0.20 cm and each 1.0 cm3 of blood contains 1.0 mg of dissolved glucose?

1.3 mg/s Fluid flow may be further characterized by the movement of fluid mass per unit time. For a noncompressible, ideal fluid with constant density (ρ), the mass flow rate (mf) quantifies the amount of mass flowing past a point within the conduit per unit time: Mass/Time mf=Q⋅ ρ

The hydrostatic weighing container above is filled with water to a depth of 2 m. If point A is 0.7 m above the bottom of the container, what is the pressure due to the weight of the water at point A? (Note: The density of water is 1,000 kg/m3.)

1.3 x 10^4 N/m^2 -P=ρgh -From the given figure, the height of the fluid above point A is the difference between the total height and the height of point A given in the question: h = 2m − 0.7m = 1.3 m

An ideal fluid flows through a tube at an initial speed of 4.0 m/s. What will be the speed of the fluid if the cross-sectional area of the tube decreases from 6.0 m2 to 2.0 m2?

12 m/s

Atmospheric pressure on a distant planet causes water to rise to a height of 10 m inside an evacuated tube with its open end immersed in a container of water open to ambient pressure. What is the atmospheric pressure? (Note: The density of water is 103 kg/m3 and the gravitational acceleration is 20 m/s2)

2 x 10^5 N/m2 Patm = Ph = ρfgh Netwons units = (kg x m)/s^2

A 10-L scuba tank is initially filled with 2,800 g of N2 gas. At room temperature (25°C), what is the pressure in the tank? (Note: Use R = 0.08 L⋅atm/mol⋅K.)

240 atm The mass of N2 is converted to moles using its molar mass. From the periodic table, the atomic mass of N is 14 g/mol. Therefore, the molar mass of N2 is (2)(14 g/mol) = 28 g/mol. Dividing the total mass of N2 in the tank (2,800 g) by its molar mass gives the moles of N2

A bone sample (specific gravity = 3) completely immersed in isopropyl alcohol (specific gravity = 0.8) is subject to a buoyant force of 4 N. What buoyant force would the same bone sample experience when immersed in water? ρ(water) = 1 kg/L acceleration due to gravity = 10 m/s2

5.0 N -specific gravity= ρ(substance) / ρ(water) -The density of isopropyl alcohol is calculated from the SG of isopropyl alcohol given in the question and the value of ρ(water) given in the passage: ρ(alcohol) = (SG of alcohol) x (ρwater) -ρ(alcohol)=(0.8)(1 kg/L)=0.8 kg/L -Fb=ρVg

What is the magnitude of the electric field generated in the acceleration chamber if the potential difference is 3,000 V over a distance of 50 cm?

6.0 kN/C E = V/d An electric field accelerates charged particles, and its magnitude has SI units of newtons per coulomb (N/C), which are equivalent to volts per meter (V/m)

What is the force felt by a doubly ionized particle in a 2,000 N/C electric field? (Note: The charge of an electron is e = 1.6 × 10−19 C.)

6.4 × 10−16 N Charged particles are accelerated in electric fields by a force known as the electric Lorentz force. The force exerted on a particle in a uniform electric field is equal to the product of the particle's charge q and the electric field strength E: F= qE

Blood flows 5 cm from Point A to Point B within an artery supplying the brain. The systolic blood pressure at Point A is 8 kPa. What is the systolic blood pressure when the blood reaches Point B? Assume the blood velocity and vessel diameter are constant over this distance. (Note: The density of blood is 1200 kg/m3 and gravitational acceleration is 10 m/s2.)

7.4 kPa The blood travels 5 cm from Point A to Point B, so hB is 5 cm greater than hA, i.e. hA − hB = −0.05 m. Substituting this value and the initial pressure into the above equation yields: PB=8000 Pa+(1200 kg/m3)⋅(10 m/s2)⋅(−0.05 m) PB=8000 kg/(m⋅s2)−600 kg/(m⋅s2) PB=7400 kg/(m⋅s2)=7.4 kPa

A charged particle is accelerated in a uniform electric field. When its velocity is 2 m/s, its electric potential energy is 100 J and its kinetic energy is 10 J. What is the particle's potential energy when its velocity reaches 4 m/s?

70 J Electric charges generate electric fields, regions of space that exert an electrostatic force on charges. The electrostatic force is conservative and the total energy E of a charged particle in an electric field is conserved. In other words, the sum of the charge's electric potential energy (PE) and kinetic energy (KE) is constant: E(initial) = E(final) PEi + KEi = PEf + KEf

Torque τ is the product of the distance r from the pivot point and the perpendicular component of the force F: τ = rFsin θ, where θ is the angle between the force and the lever arm. The magnitude of sin θ (and torque) is greatest when θ is:

90°

dielectric constant

A dimensionless number that indicates the factor by which capacitance is increased when a dielectric is placed between its plates.

adiabatic process

A process in which no heat is transferred to or from the system by its surroundings.

Which of the following best describes a high voltage plate if it accelerates positive ions away from it? A. It is positively charged, and its electric field lines point away from it. B. It is positively charged, and its electric field lines point toward it. C. It is negatively charged, and its electric field lines point away from it. D. It is negatively charged, and its electric field lines point toward it.

A. It is positively charged, and its electric field lines point away from it. For the positive ion to be accelerated away from the plate, the charge on the plate needs to repel the ion. Charges with the same sign repel each other. Electric field lines are used to denote the direction that a positive charge would be accelerated in an electric field. Because positive charges repel positive charges, electric field lines point outward from positive charges and point toward negative charges

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 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.

Doppler effect

An observed change in the frequency of a wave when the source or observer is moving

A dielectric material is introduced into the empty space between the two plates of a parallel plate capacitor. How will the capacitance (C) change if the value of the dielectric constant (κ) for the material is 1.5? A. C will decrease by 33%. B. C will not change. C. C will increase by 50%. D. C will increase by 100%.

C. C will increase by 50%. The dielectric constant (κ) reflects the ability of dielectrics to increase the functional capacitance beyond the capacitance in a vacuum (C0), defined as the absence of any material. This relationship is expressed as: C = κ⋅Co

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.

C. continues along her original path while spinning about her center of mass.

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)

C.(F)(2L) -friction is a nonconservative force -the work done by friction equals the change in the total mechanical energy (the sum of PE and KE): Wf=ΔE -Wf depends on the total distance through which the force is applied rather than the displacement -The total amount of work done equals the sum: Wf= Wf,down + Wf,up Wf= (−FL)+(−FL) = −(F)(2L)

Henry law of solubility

C=(kH) x (Pgas) where C is the concentration of the dissolved gas, and kH is the solubility coefficient specific to the gas and solution at a given temperature

speed of light equation

C=λv where λ is the wavelength of a photon, v is the frequency of a photon, and C=3.00*10^8 m/s

right hand rule

Common method used to determine the direction of the magnetic force vector. Thumb points in the direction of charge's velocity, fingers point in direction of magnetic (B) field, palm points in the direction of the acting force.

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

D. Reflection Refraction, the bending of light, occurs at the boundary between two different mediums with different values of n. 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

The electric force generated by two point charges separated by Distance A is 4 times greater than the electric force generated when separated by Distance B. How does Distance A compare to Distance B?

Distance A is shorter by a factor of 2 moving from Distance A to Distance B decreases the electric force by a factor of 4. According to Coulomb's law, this relationship would be observed when Distance A is shorter than Distance B by a factor of 2

energy of light

E = hf or (hc)/λ h= Planck constant

First Law ofThermodynamics

Energy cannot be created or destroyed; it can only transfer from one form to another 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

For a floating object, the fraction submerged is equal to:

Equal to the ratio of the density of a floating object to the density of the liquid fraction submerged=ρ (object)/ρ (fluid)

Force of an electric field

F= Eq ***** everyone quits*

Newton's Second Law of Motion

Force = mass x acceleration (F=ma) -a force exerted on a mass will cause it to accelerate -the acceleration of an object depends on the net force acting upon the object and the mass of the object

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:

Fs = (μs)N μs = coefficient of static friction (a number unique to the two surfaces) N = normal force (the perpendicular force one surface exerts on the other)

The resistance of an object acting as a resistor is directly proportional to its: I. resistivity. II. cross-sectional area. III. length.

I and III only The resistance of a given object quantifies the relative difficulty by which charge moves from one end of the object to the other. As a result, resistance increases in direct proportion to length (L) because increased length forces charge to travel through a greater distance of resistant material. Conversely, resistance decreases as the cross-sectional area (A) increases because additional cross-sectional area provides more parallel channels through which electrical charge can flow.

Boltzmann equation

KE = 3/2 x Kb (boltzmann constant) x T (temperature)

An object is launched with a one-time burst of propulsion away from the surface of the Moon. After the burst, what happens to the KE and PE of the object as it moves away from the Moon's surface?

KE is converted into PE -After the object (eg, a rocket) is launched from the Moon, the only force present in the system is gravity. Therefore, work done by gravity progressively decreases the velocity and the KE of the object. KEi > KEf -Simultaneously, the PE of the object increases (becomes less negative) as the radial distance from the mass increases: PEi < PEf The decrease in the KE of the object is accompanied by an increase in the PE of the object such that conservation of energy is maintained.

3 types of thermodynamic systems

Open: allows heat and matter to be exchanged with the surroundings Closed: allows heat but not matter to be exchanged with the surroundings Isolated: does not allow heat or matter to be exchanged

Power equation

P= W/t (work/time)

Ideal Gas Law

PV = nRT P = pressure in atmospheres V = volume in liters n = number of moles R = gas constant T = temperature in Kelvin

hydrostatic pressure

Pressure exerted by a volume of fluid against a wall, membrane, or some other structure that encloses the fluid.

Types of State Functions

Pressure, density, temperature, volume, enthalpy, internal energy, Gibbs free energy, and entropy

Bernoulli's Equation

P₁+ρv₁²/2+ρgy₁=P₂+ρv₂²/2+ρgy₂ where P=absolute pressure, ρ=density, and y=height relative to the reference height

relationship between temperature and radiation

Radiation energy is directly related to the temperature of the object that emits the radiation. Hotter objects radiate waves in the higher frequency region of the spectrum; conversely, colder objects radiate waves in the lower frequency region

mechanical advantage

Ratio of the output force exerted by a machine to the input force applied to the machine. MA = output force/input force

vasoconstriction

Reduces blood flow and heat transfer by decreasing the diameter of superficial blood vessels.

Convection

The transfer of heat through the *flow of fluids*. Fluids absorb heat from hotter regions and deliver it to colder regions

Energy stored in a capacitor

U=1/2CV^2

index of refraction

a measure of the amount a ray of light bends when it passes from one medium to another n = c / v c: speed of light in a vacuum v: speed of light in the medium

Boltzmann's constant

a physical constant relating the average kinetic energy of particles in a gas with the temperature of the gas; it is the gas constant R divided by Avogadro's number (1.38x10^-23 J K^-1)

The absolute temperature of ideal gas molecules stored in a container is directly proportional to the:

average kinetic energy of gas molecules

A system is in thermodynamic equilibrium with another system or its surroundings if:

both have the same temperature

surface tension arises from

cohesive forces (b/w like molecules) in a fluid

Because potential energy is related to position and not path, potential energy is associated with

conservative forces (eg, gravitational, electrostatic, elastic forces) -the work performed is independent of the path taken -the work done by a force only depends on the initial and final positions of the object

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 sample of water vapor undergoes deposition and then melting. What happens to its entropy after each phase change?

decreased with deposition (gas to solid), increased with melting

An ideal fluid flows within a fixed tube with decreasing cross-sectional area. Assuming constant height and volumetric flow rate, what effect does this have on fluid pressure and fluid velocity?

fluid pressure decreases fluid velocity increases

ΔH is the net amount of energy (heat) released or absorbed from the:

formation and destruction of chemical bonds in a reaction

Pascal Law states that the pressure on a ______fluid is transmitted undiminished to every portion of a container.

incompressible (constant density), and fully enclosed fluid

Heat transfer from an organism to the environment can be accomplished by:

increasing superficial blood flow (enhancing thermal conduction) or by increasing respiration (enhancing conduction and convection)

relationship between frequency and period

inversely related f= 1/T

Water has relatively high surface tension compared to many liquids due to:

its ability to form hydrogen bonds

the work associated with the expansion or compression of a gas

known as pressure-volume work, which is calculated as the product of the external pressure (P) and the change in volume (ΔV): *W=PΔV*

Periodic motion (object moves in a cyclical fashion) is modeled in terms of wave motion, where the time required to complete one cycle of motion is defined as the:

period (T)

The orbital motion of a mass around a central body is

periodic

heat capacity equation

q = mCΔT

Which expression gives the radius of curvature in a magnetic field B for the path of an ion with a mass of m, charge of q, and velocity of v? The centripetal force F exerted on an ion: F= mv/r^2

r = (m/q) x (v/b) The force exerted on a moving particle in a magnetic field is known as the magnetic Lorentz force, and it is equal to the product of the particle's charge, velocity, and strength of the magnetic field: F = qvB.

When a substance undergoes a phase transition, it absorbs (or releases) heat and its temperature _________________ until the entire substance has transitioned to the new phase.

remains constant

Capacitance

the ability of a capacitator to store energy in the form of electrically separated charges

The work-energy principle states that the total work W done by a force is equal to

the change in kinetic energy (ΔKE) of the object acted upon by the force: W= ΔKE

relationship between potential energy and work

the change in potential energy (ΔU) is equal and opposite to the work (W) done by conservative forces within the system: ΔU=−W

An ammeter in series with a circuit component measures

the electric current flowing through it

Law of Conservation of Energy

the law that states that energy cannot be created or destroyed but can be changed from one form to another -ΔKE= −ΔPE -ΔKE + ΔPE = 0 -(KEf−KEi) + (PEf−PEi) = 0 -KEi + PEi = KEf + PEf

The normal force, N is the perpendicular force one surface exerts on another. On a horizontal surface the normal force is equal to

the objects weight (W=mg)

Potential energy depends on

the position of objects within the system

If the forces acting on an object are conservative forces (eg, gravity), then the work done by the force also contributes to a change in:

the potential energy of the system (ΔPE): W= −ΔPE

Torque

the rotational force that makes objects spin about a pivot point τ = rF sin θ τ= F x d

Dalton law of partial pressure

the total pressure of a mixture of gases is equal to the sum of the partial pressures of the component gases

Archimedes' principle states that the magnitude of the buoyant force (Fb) that acts on a floating object is equal to:

the weight of the fluid displaced by the object

state function vs process function

State: a function that depends only on the initial and final states of a system, not on the path in between. Process: describe the pathway from one equilibrium state to another (ex: work and heat)

thermal conductivity

The ability of an object to transfer heat to another object

heat capacity

The amount of heat required to raise the temperature of a specified amount of a substance by 1°C or 1 K.

Conduction

The direct transfer of heat from one substance to another substance that it is touching.

Which is higher: the molar heat capacity of a gas at constant pressure or the molar heat capacity of a gas at constant volume?

The molar heat capacity of a gas at constant pressure *exceeds* the molar heat capacity of a gas at constant volume. 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. Therefore, allowing a previously fixed piston to move freely (to maintain constant pressure) will increase the molar heat capacity of a monoatomic ideal gas.

An object with the same density as water is stationary and suspended in a container filled with water. A downward force is momentarily applied to the object. Assuming the water density remains constant and ignoring the effects of fluid friction, what will happen to the object immediately after this downward force is removed?

The object will sink at a constant velocity -When a mass experiences a net force, the mass will accelerate in the direction of the force (F = ma). -When no net force acts on an object, its velocity remains unchanged. -Therefore, an object will accelerate to a velocity when a force is applied and will continue at the same velocity after the force is removed. -Newton's 1st Law: an object at rest will stay at rest, and an object in motion at a given velocity will stay in motion at the same velocity