Physics Reading
What is the Big 5 Equations that has missing Distance?
(Velocity) = (Initial Velocity) + (Acceleration x Time)
What are the steps for solving a pulley problem?
1. Draw the Force Diagram 2. Choose the Direction of Movement (+) 3. Find Fnet and set it equal to ma.
What are the two main functions of a parallel plate capacitor?
1. To create a unifrom electric field 2. To store electric potential energy
How is Resistors in Parallel Calculated?
1/Req = 1/R1 + 1/R2 + 1/R3 ...
A crate weighs 1000N on a horizontal floor. Static coefficnet of friction is 0.4. If you push with 250N, what is the magnitude of the force of static friction?
1000* .4 = 400N, However we push with 250N therefore magnitude = 400N
A piece of rubber is 18 cm long and is streched to 20 cm. What strain has it undergone?
2/18 = 1/9
An air capacitor is charged and disconnected from the battery. The electric field between the plates is E. Now, a dielectric with a dielectric constant K = 4 is inserted between the plates. What is the electric field created by the layers of induced charges on the surfaces of the dielectric?
3E/4 opposite the direction of E Note that it is asking for Einduced! E-Einduced = Resulting E Therefore, Resulting E = E/K thus Einduced is 3E/4.
What is an Isochoric Process?
A process that maintains a constant volume.
What is a Perfectly Inelastic Collision?
An Inelastic Collision where the objects stick together afterwards.
If you have nearsightedness, where are the rays of light being projected? Before or Past the Retina?
Before the Retina
Two objects are subjected to identical tensile stresses. The object with the great value of Young's Modulus will undergo: A. Smaller Change in Length B. Greater Change in Length C. Less Strain D. Greater Strain
C. Can't say anything about length since we do not know the original lengths of the objects
How is Capacitors in Series Calculated?
Ceq = 1/C1 + 1/C2 + 1/C3 ...
A particle with a negative charge, -q, with a speed vo enters a region containing a magnetic field. Is the speed increased, decreased, or constant through this field?
Constant! Magnetic Forces do no work.
A 1N apple in a tree 4 meters above the ground. The apple falls. What is the change in the apple's potential energy?
Direction of Falling and Gravity are in the same direction, therefore, Negative Value! -4J
The charge on a parallel plate capacitor is 4 x 10^-6. If d = 0.002 m and 1 microfarad, whats the electric field strength?
E = 2000 V/M Q = C * V and V = Ed
T or F: Work is a vector.
False Work is a scalar.
What is the Force due to Gravity acting Parallel to an Inclined Plane?
Force = mg sin (Theta)
What is the Impulse-Momentum Theorem?
Impulse = Delta Momentum = Delta Velocity x Mass = Force x Delta Time
What amount of work does Kinetic Friction do? Static Friction?
Kinetic -> Always Negative Static -> Always Zero
What is Myopia?
Nearsightedness
A car drives to a location with an average speed of 30 m/s and makes the return trip with an average speed of 40 m/s. What is the magnitude of the car's average speed for the entire trip?
The magnitude of the car's average speed for the entire trip is 34 m/s. Since distance equals average speed multiplied by the time, the time for the first half of the journey is D / 30 and the time for the second half of the journey is D / 40. Therefore, the average speed would be 2D / ((D / 30) + (D / 40)). A simpler way to solve this would be to choose a value for D, say 120 m. In this case, the average speed would be 2(120) / ((120 / 30) + (120 / 40)) which equals 240 / 70, or roughly 34 m/s. Since the 30 m/s segment takes the longest, it should count more than the 40 m/s segment. The average speed, therefore, should be less than 35 m/s. 34 m/s is the only non-zero answer choice that is less than 35 m/s.
A charged capacitor has a charge Q, and the voltage between the plates is V. What will happen to C if Q is doubled?
Think Q = C * V Nothing will happen, For a capacitor, C is constant. V will double however.
T or F: Dielectrics for Capacitors always increase Capcitance.
True
If given Velocity and Force, how does one calculate Work?
Velocity x Force = Work
What is the Work-Energy Theorem?
Wtotal = Delta Kinetic Energy
How do we calculate Centripetal Acceleration? Centripetal Force?
a = (v^2)/r Then F=ma Therefore, F = m x (v^2)/r
How do we calculate Torque?
t = r x F x Sin(Theta)
The charge on the capacitor is Q, and the capacitance is C. If the electric field in the region between the plates has magnitude E, which of the following expressions gives the time required for the proton to move up to the other plates?
v = d * SQRT(2mC/eQ)
Three Blocks hang from a mass-less stick. M1 = 2 kg at 20 cm (Left Side) M2 = 5 kg at 70 cm (Right Side) M3 = 3 kg at 80 cm (Right Side) What mark should a string lay so that the system is balanced?
(x-20) x (2) = (70 - x) x (5) + (80 - x) x (3) x = 63 kg
How do you calculate a Center of Mass problem? What is the equation?
1. Choose a point of reference (x=0) 2. Determine locations of objects X1,X2... 3. Multiple Each Mass by Location 4. Divide by total mass M1+M2...
For Delta Kinetic Energy, Explain how you would calculate this.
Square each individual velocity before subtracting! Delta K.E. = (1/2) x M x ((V1 ^ 2) - (V2 ^ 2))
What is Rotational Inertia?
Tells us how resistant the object is to rotational acceleration. (More Mass away from Rotational Axis) (Symbol = I)
What is the First Law of Thermodynamics?
The Total Energy of the Universe is Constant.
What is Mechanical Advantage?
(Resistance Force) / (Effort Force) Effort Force = Force Applied w/ Machine Resistance Force = Force Applied w/o Machine
An object has an Initial Velocity of 3, Acceleration of 2, What is the object's Velocity at Time = 6 ?
(Velocity) = (Initial Velocity) + (Acceleration x Time) Ans: Velocity = 15
What is the Big 5 Equations that has missing Time?
(Velocity) ^ 2 = (Initial Velocity) ^ 2 + 2 x (Acceleration) x (Distance)
A block is sitting at rest on a horizontal table. According to Newton's Third Law, Indicate the correct action-reaction pairs of the forces?
1. The weight of the black and the gravitational force exerted by the block on Earth 2. The Normal Force exerted by the block on the table and the Normal Force exerted by the table on the block 3. The gravitational force exerted by the table on the block and the gravitational force exerted by the block on the table
Ethyl Alcohol has a PG of 0.8. If a cork has a SG of 0.25. What fraction of the cork's volume is submerged?
5/16
A brick that weighs 25N is lifted from the ground to the shelf that is 2 meters high? What is the change in gravitational potential energy?
50 J
Approximately how much upward force should be applied to a 60 kg person at sea level to achieve 5g?
5g - g (What we already experience) = 4g Therefore 40m/s2 * 60 kg = 2400 N
A metal sphere with no net charge is placed near a positive source charge. All of the following are true EXCEPT: A. The electric field inside the sphere will not be zero because the sphere has an uneven charge distribution. B. The sphere will be attracted to the source charge. C. The net electric force between the sphere and the source charge is not zero. D. The source charge will force the electrons on the sphere to move.
A. Since the sphere now has a positively charged side and a negatively charged side, there is an induced electric field within it that perfectly cancels the external field (this is the field-focused way of explaining why the charges redistribute in a conductor, to cancel the external field). This makes choice A false, and the correct answer.
T or F: Light and Sound Waves can travel through a vacuum.
False Sound waves are mechanical, so they need a medium through which to travel. Light waves are electromagnetic and do not need a medium.
Suppose one moves 10 times further away from a loud siren of constant power. What is the resultant decrease in sound level? A. 10 dB B. 20 dB C. 40 dB D. 100 dB
B. Increasing distance by a factor of 10 decreases intensity by a factor of 100, whcih is 10 x 10. Therefore, sound level will be reduced by 10 + 10 = 20 dB.
At point p the electric potential due to source charge Q is 360 V. If p is a distance r from Q, what is the electric potential at a point 2r from Q? A. 90 V B. 180 V C. 360 V D. 720 V
B. The electric potential from a source charge at a point is given by φ = kQ / r where r is the distance between the point and the source charge and k is Coulomb's constant. Since the potential is inversely proportional to the distance, doubling the distance will halve the potential.
Point charge A exerts a force of 36 N on point charge B which is 30 cm away. If charge B is moved 60 cm further away from charge A, what is the force exerted by charge A on charge B? A. 1 N B. 4 N C. 9 N D. 12 N
B. (I Choose C.) The equation to calculate the force between two point charges is F = k|QA||QB| / r2. The result of QB moving 60 cm further away is that it will be 90 cm away. Since r increases by a factor of 3 (from 30 cm to 90 cm) then F decreases by a factor of 9 (since r is in the denominator and squared, F is inversely proportional to r squared). Since F was 36 N and decreases by a factor of 9, then the new force is 36 / 9 = 4 N. Algebraically, FNew = kQAQB / (3r)2 = (1/9)(kQAQB / r2) = (1/9)(36) = 4 N.
All of the following are true of an electric field EXCEPT: A. The strength of an electric field created from a source charge is inversely proportional to the square of the distance from the source charge. B. The electric field created from a source charge is equal at any point of equal distance from the source charge. C. The electric field is strongest where the field lines are densest. D. A positive charge in an electric field will experience a force in a direction tangent to the field lines.
B. (I Choose D.) An electric field is a vector field. The field lines indicate the direction of the force on a positive test charge, so choice D is true and can be eliminated. At any point around a constant radius from Q, the magnitude of E will be constant, but the direction of E will be different, so choice B is false and the correct answer.
A dipole consists of two charges separated by a distance of 2 m. The charge on the left is 2 nC and the charge on the right is -2 nC. What is the value of the electric potential at a point halfway between the two charges? A. -18 V B. 0 V C. 18 V D. 36 V
B. (I Choose D.) The electric potential ? from a source charge Q at any distance r from the source charge is ? = kQ / r where k is Coulomb's constant. The principle of superposition states that the electric potentials of multiple source charges can be added. The only difference between the potentials from each charge is the sign due to the charge, and as potential is a scalar, the sum must therefore be zero. The calculations are as follows: the electric potential from the left source charge is ?Left Q = (9 × 109)(2 × 10-9) / 1, = 18 V, and the electric potential from the right source charge is ?Right Q = (9 × 109)(-2 × 10-9) / 1, = -18 V. Therefore the total electric potential is 18 V - 18 V = 0 V.
A sailboat sailing on a freshwater lake ran into a buoy. If the buoy's specific gravity is 0.75, what proportion of the buoy was above the water at the time of impact? A. 1/8 B. 1/4 C. 1/2 D. 3/4
B. (I Choose D.) To get the proportion of a floating object that is submerged, use Vsubmerged / V = ρobject / ρfluid. The question gives specific gravity, which is the density of the object divided by the density of water. Hence, Vsubmerged / V = 0.75, which means that 3/4 of the object is submerged. The question asks for the proportion above the water, which is the remaining 1/4 or 0.25.
If a candle is placed beneath a rigid container containing a gas, what is the sign of heat and work for this process? A. Heat is positive, work is positive. B. Heat is zero, work is negative. C. Heat is positive, work is zero. D. Heat is negative, work is zero.
C. The keyword "rigid" indicates that there is no volume change. No change in volume means that no work is being performed (eliminating choices A and B). The addition of a candle beneath the container means that heat is going from the surroundings into the system, which is a positive heat change. Thus, choice C is correct.
What is Hyperopia? (Hypermetropia)
Farsightedness
Relative to the typical dropping parachutists, one who thrusts himself downward on exiting the airplane (ignoring air resistance and assuming both parachutists open their parachutes after the same amount of time) will have: A. Lower A and Same V B. Same A and Same V C. Same A and Higher V D. Higher A and Higher V
C. Since Higher Initial Velocity but same constant A (Not D since Force is initially there, not for the full duration)
A 100 kg Bungee Jumper is 30 meters from equilibrium on a 100kg/s2 elasticity constant rope. What is his acceleration in the spot? A. 0 B. 10 C. 20 D. 30
C. (I Choose D.) F = k * x and F= MA DONT FORGET GRAVITY FORCE Fb = (100)(30) and Fg = (100)(10) Ft = Fb - Fg = 2000N F=ma therefore a = 20
A test charge q has a velocity of 40 m/s at point A (electric potential of 300 V). The charge slows to a stop at point B (electric potential of -100 V). If the mass of the charge is 10-6 kg, what is the charge on q? A. 2 × 10-6 C B. 4 × 10-6 C C. -2 × 10-6 C D. -4 × 10-6 C
C. (I Had NO Idea) Since the charge begins with a velocity and slows to a stop, the velocity and final kinetic energy are zero. The change in kinetic energy is all the initial kinetic energy so KE = (1/2) mv2 = (1/2)(10-6)(40)2 = 8 × 10-4. This loss in kinetic energy is the same as the gain in potential energy. The gain in potential energy is ΔPE = qV and solving for q yields q = ΔPE / V = 8 × 10-4 / (-100 - 300) = -2 × 10-6 C. Note that the charge must be negative since it is losing kinetic energy and gaining potential energy while moving to a lower potential.
How would the net force on an object undergoing uniform circular motion have to change if the object's speed is doubled?
Centripetal Force = m x (v^2)/2 Therefore, Net Force would have to increase by 4.
How is Capacitors in Parallel Calculated?
Ceq = C1 + C2 + C3 ...
A parallel-plate capacitor, with air between the plates is charged to a voltage of V=1000 V by a battery. The values Q, E, and PE are measured. When a dielectric is inserted and the battery is removed, what values are constant, which are reduced?
Constant = Charge (Q) Reduced by K of Dielectric = Electric Field (E), Voltage (V), and Potential Energy (PE)
What direction does current go? Is this the same or opposite direction of electrons?
Current -> Towards - End Electrons -> Towards + End Therefore Opposite Directions
What is the Big 5 Equations that has missing Acceleration?
D = (1/2) x (Initial Velocity - Velocity) x (Time)
What is the Big 5 Equations that has missing Velocity?
D = (Initial Velocity) x Time + (1/2) x (Acceleration x Time) ^ 2
An object is dropped from 80 meters in the air. Time to hit ground?
D = (Initial Velocity) x Time + (1/2) x (Acceleration x Time) ^ 2 Ans: T = 4
What is the Big 5 Equations that has missing Initial Velocity?
D = (Velocity) x Time - (1/2) x (Acceleration x Time) ^ 2
When rapidly turning a corner on a flat road, a cyclist leans into the center of the turn. The frame of the bike is nearly parallel to which vector? A. The Force of Gravity on the Bicycle and Rider B. The Normal Force on the Pair C. The Centripetal Force D. The Sum of the Normal and Friction Forces
D. A. is Wrong, Gravity is always Pointed Down B. is Wrong, Normal Force is always perp to the surface (Up in this case) C. is Wrong, Centripetal Force is towards center, therefore parallel to the flat road D. is Correct, Bike at Angle = Sum of C. (Friction = Centripetal Force) and B.
Three Light bulbs are connected in parallel to a battery. If one burns out, what will happen? A. The other two bulbs will go out B. The other two bulbs intensity will decrease. C. The other two bulbs intensity will increase. D. The other two bulbs intensity will stay the same.
D. I = V/R, then P = V * I^2 .... So if the R is constant for a single light bulb, and V is constant, then I will be constant making P constant. The overall circuit current will decrease, from the total resistance increasing, but this will result in less overall current to the circuit, not to each individual light bulb.
What is the Acceleration of a Block down a Frictionless Plane, with the only Forces acting on the block being Gravity and Friction?
Fgrav = mg x Sin (Theta) Ffric = µmg x Cos (Theta) F = ma Therefore, a = µg x Cos (Theta) x g x Sin (Theta)
An arctic tern is soaring without flapping its wings. Which of the following explain how the tern is able to stay aloft? A. The distance air must travel under the wings is greater than over the wings, increasing the pressure below the wings B. The distance air must travel under the wings is greater than over the wings, decreasing the pressure below the wings C. The distance air must travel over the wings is greater than under the wings, increasing the pressure above the wings D. The distance air must travel over the wings is greater than under the wings, decreasing the pressure above the wings
D. (I Choose A.) This is a typical two-by-two question. The Bernoulli Effect says that the greater the speed, the lower the pressure. In this case, the pressure below the wings must be greater than the pressure over the wings. The difference in pressure between the bottom and top of the wings causes lift, allowing the tern to stay aloft.
A dipole consists of two charges separated by a distance d. The charge on the left is +Q and the charge on the right is -Q. What is the value of the electric field at a point 1/3 d from +Q and 2/3 d from -Q? Use k for Coulomb's constant. A. (9/4) kQ / d2 B. (27/4) kQ / d2 C. 9 kQ / d2 D. (45/4) kQ / d2
D. (I Choose B.) The strength of the electric field E from a source charge Q at any distance r from the source charge is E = k|Q| / r2 where k is Coulomb's constant. The principle of superposition states that the electric fields of multiple source charges can be added. The electric field from the left source charge is ELeft Q = kQ / (d/3)2 = 9 kQ / d2. The direction of ELeft Q is away from the positive charge and toward the negative charge (the direction of force a positive test charge would feel), which is to the right. The electric field from the right source charge is ERight Q = kQ / (2d/3)2 = (9/4) kQ / d2. The direction of ERight Q is away from the positive charge and toward the negative charge (the direction of force a positive test charge would feel), which is still to the right. The total electric field is the sum of these two fields 9 kQ / d2 + (9/4) kQ / d2 = (45/4) kQ / d2 to the right. Note that the full math is not necessary because once it is known to be 9 + something, choice D is the only possible answer.
An electric eel is swimming in an aquarium's pressurized tank. The pressure above the fresh water is 125 kPa. If the eel is 15 m deep in the tank, what is the total pressure experienced by the eel? A. 125 kPa B. 150 kPa C. 200 kPa D. 275 kPa
D. (I Choose C.) Total pressure is the sum of hydrostatic gauge and the pressure above the water. Ptotal = Pgauge + Pon top = ρfluidgD + 125 kPa = 1000 kg/m3 × 10 m/s2 × 15 m + 125 kPa = 150000 Pa + 125 kPa = 150 kPa + 125 kPa = 275 kPa.
What is the Equation for Newton's Law of Gravity?
F = G * (Mass 1) * (Mass 2) / (Radius Between Them) ^ 2
T or F: Light and Sound Waves travel faster through water than through air
False Longitudinal waves travel faster through a more incompressible medium, sound travels faster through water than through air. In contrast, light travels faster through air than water.
T or F: Light and Sound Waves can travel through a vacuum
False Sound waves are longitudinal and cannot be polarized, whereas light waves are transverse and can be polarized.
What is the Acceleration of a block down a frictionless plane, with No External Force but Gravity pushing it?
Force = Mg sin (Theta) F=ma Therefore, a = g * sin (Theta)
What is the Force due to Gravity acting Perpendicular to the Inclined Plane?
Force = mg cos (Theta)
What is the Zeroth Law of Thermodynamics?
If one object is in thermal equilibrium with a second object, and the second object is in thermal equilibrium with a third object, then the first and third objects are in thermal equilibrium with each other.
What is Wave Speed?
It is the speed at which waves can travel (Think about a guitar.. Waves have a fixed Wave Length, therefore increasing tension will increase wave speed).
A sound wave of frequency 440 Hz travels at the speed of 344 m/s through air. How much faster will the wave travel if the frequency was 880 Hz?
It will still be 344 m/s Altering frequency will not affect the wave speed.
What is the Equation for Angular Momentum?
L = I x Omega or L = l x m x v
Imagine two balls, same mass, Ball 1 is uniformly distributed with mass, but Ball 2 is hollow in the center and mass squished to outside. Which has the greater Rotational Inertia (I)? Which is harder to roll?
More Mass Distribution = Greater I Therefore, Ball 2 = Higher Rotational Inertia, and harder to roll
Image the Following Magnets: (S)---(N) * (S)----(N) If the star is a particle traveling at velocity v, then what direction is the Magnetic Force exerting a force?
Out of the Page Magnets go from North to South (->) Velocity is Down v X B, therefore force is out of page.
The speed of a 2 kg mass on a spring is 4 m/s as it passes through its eq position. What is teh frequency if the amplitude is 2m?
PE = KE (0.5)(k)(x^2) = (0.5)(m)(v^2) Solve for k ... k = 8 use Period Formula .. T = (2)(pi)SQRT(m/k) T = 3 therefore Frequency = 1/3
If you have farsightedness, where are the rays of light being projected? Before or Past the Retina?
Past the Retina
What are the units of Capacitance? Equation?
Q = C * V C -> Capacitance -> [C/V] Colombs / Volts or Farrad
What is the main equation used in Capacitor Circuits? Units of the variables in the equation?
Q = C * V Q = Colombs / Time C = Farrads V = Volts
Consider a charge q+, initially at rest near another charge Q. How would the magnitude of the electic force on +q change if Q were moved away, doubling the distance?
R = 2 Therefore F will decrease by 4
How is Resistors in Series Calculated?
Req = R1 + R2 + R3 ....
What material has the greater Young's Modulus: Rubber or Glass?
Rubber = Flexible Therefore, Glass has higher Young's Modulus
What is the simple observation for pulleys on the MCAT?
The pulley system (with massless, frictionless pulleys) causes a constant tension to exist through the entire string, which can lead to multiple tension forces pulling on an object.
What if when calculating Total Mechanic Energy, there is an associated Friction Force?
The resulting equation will be: KE + PE + Work by Friction (Usually -) = KE + PE
What has a higher Shear Modulus and Young's Modulus? A material with a lot of intermolecular forces, or a small amount?
The stronger the intermolecular forces, the greater the modulus. (p. 243)
What is Centripetal Force?
This is the NET force directed towards the center that acts on an object to make it execute uniform circular motion.
What is Centrifugal Force?
This is the NET force directed towards the outside of the circular motion.
T or F: An object moving in a circular path is said to execute uniform circular motion if its speed is constant.
True
T or F: The work done by gravity depends only on the initial and final heights of the object, not on the path the object follows.
True
T or F: When a string vibrates in its nth harmonic mode, it means there are n half-wavelengths along the length of the string.
True
T or F: Light and Sound Waves can experience reflection, refraction and diffraction.
True Both sound and light waves experience wave properties that are not dependent upon the transverse versus longitudinal distinction, such as reflection, refraction and diffraction.
What is the equation for Work?
W = F x d x Cos(Theta)
What is an Elastic Collision?
When the Total Momentum and Total KInetic Energy is Concerved.
What is an Inelastic Collision?
When the Total Momentum is conserved but total Kinetic Energy is not.