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106 Cards in this Set

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  • Back
Can an object be accelerating even if its speed is constant?
Yes, such as centripetal motion (direction is constantly changing => velocity is changing and therefore there is acceleration)
What direction does the acceleration have to point in reference to the initial velocity if the speed is decreasing?
acceleration points in the direction opposite to the initial velocity
If acceleration has a perpendicular aspect, what is occuring? What should you do?
If acceleration has a perpendicular aspect, then direction is changing. You should cut it up into its components.
What are the big five equations?
d=v_i t +0.5at^2
Mneumonic for missing parts: A dog finally in tears
What does the slope of a position vs. time graph represent?
The slope of a position vs. time graph gives the velocity
What does the slope of a velocity vs. time represent?
slope of a velocity vs time graph gives acceleration
What does the area under a velocity vs time represent?
area under a velocity vs. time graph gives the displacement
What should you do when you analyze projectile motion?
Analyze projectile motion separately in its x and y components; if the horizontal acceleration is zero thruout the projectile's flight, then the horizontal velocity will be constant throughout the flight.
When must you always be conscious of when dealing with a projectile's total flight time?
Make sure that the projectile's total flight time will be 2x the time required to reach the top. (vf=0)
What is Newton's 1st state?
Newton's First law: object at rest will remain at rest. Object moving will continue to move w/ constant velocity unless a force acts on the object.
What is Newton's 2nd law? What are potential MCAT traps?
MCAT Traps:
* Understand why an object will not always move in the direction of Fnet (direction of an object's velocity is not given… just the acceleration)
* undestand that Fnet=0 doesn't necessarily mean that v=0.
What is newton's 3rd law state? ** reread page 33
same magnitude but opposite direction forces. (Action reaction pair) -- doesn't say that the effects of these forces will be the same. (ie. On acceleration b/c of differences in masses) REREAD PAGE pg 33
What is a commonly tested right angle triangle on the mcat? (3-#-# triangle.)
3-4-5 triangle
What is the difference between static and kinetic friction? Which is greater?
static-friction and kinetic (or sliding) friction...

Static friction usually > than kinetic friction... it's called MAXIMUM force on static friction; always opposite to the dir of the object's intended velocity.
What is the normal force?
The normal force is the perpendicular component of the contact force exerted by a surface on an object. Fn is the perp comp of the contact force exerted by a surface on an object, while the friction force is the parallel comp of the contact force exerted by a surface on an object.
Where is theta on an incline plane?
Is the angle between the normal force (mgcos theta) and the weigth (mg).
What is a pully like?
pully is like multiplying our force by however many strings are pulling on the object
What is the formula for gravitational force? What is gravity if set w=F_grav?
F_grav= (G M m) / (r^2)

since w=F_grav => g=G M / r^2
What is the formula for kinetic and maximum static friction?
F_f=u_k F_n
F_f,max=u_s F_n
What are the forces for incline plane (normal force and force due to ravity acting parallel to inclined plane)?
parallel to inclined plane: mgsin (theta)

normal force exerted by inclined plane: mg cos(theta)
How do you find the center of mass of something?
How does the weight of the meter stick effect the CM?
x_cm= (m1*x1 + m2*x2 + m3*x3)/(m1+ m2 + m3)

First choose an origin (a reference point that you will call x=0); the locations of the objects will then be measured relative to this point. Determine the locations x1,x2,x3 etc of the objects. Multiply each mass by itslocation and then add. Then divide by the total mass.
*** weight of the meter stick changes the value of the CM (remember that you should include the weight in the denominator and numerator… gets neglected from numerator if set origin at 0.
What is the center of gravity? How do you find it?
point at which the total gravitational force on the system can be considered to act. THE OBJECTS masses are replaced by their weights.
What are the properties of uniform circular motion in terms of speed and acceleration?
- spead is constant but velocity is changing constantly (b/c different direction) ==> therefore, see that acceleration is present despite speed being the same
- acceleration always points towards the center of the circle;
- v is always tangent to the circle.
What is the magnitude of centripetal acceleration?
magnitude of centripetal acceleration: a=v^2/r

The force is F=mv^2/r
What do you have to pay attention about with regards to relationship btw Fnet and the parameters acceleration and velocity?
Make sure you undestand again that it's the direction of the acceleration not the velocity that always matches the direction of Fnet.
The centripetal force is in what direction. What sign should this have?
- Do not add a force called Fc in your picture…
- Always call toward the center the positive direction. Any force toward the center are then positive forces and any forces directed away from the center are negative.
- Look at example 3-8
What is equation for torque? What are the units?
Torque = rFsin(theta) pg 66
Units are N*m.
- When calculating torque, what are the intricacies about theta?
- What happens torque when r is perpendicular to F?
- What direction of rotation denotes positive and negative torque?
Don't need to worry about which theta to take since they're supplements.

If r is perp to F, then torque=rF;

CCW rotation is positive and CW is negative.
Is displacement a vectory quantity?
What is the difference btw speed and velocity?
Velocity is a function of displacement. Displacement only cares about initial and final point.
Q: A particle moving along the x axis passes through the point x=0 (in the -x direction) at a particular instant. If it experiences a constant acceleration of -2m/s^2, where could the object be 3s later?
A. x=-3
B. x=-6
C. x=-9
D. x=-12
PG 236 #27; if it started at rest, it would be x=-9 but since it was moving, x should be less and therefore D) is the only answer.
Do you need to know the actual angle if you're doing incline problems?
No, you can just say sin(theta)=O/H and have that as your sin(theta).
Pendulum problem. What is the speed at the lowest point if dropped from ...?
loss of gravitational potential energy equals the gain in kinetic energy: mgh=0.5mv^2
What is the work-energy theorem?
The total work done on an object is equal to the change in its kinetic energy. (W_total=delta(KE)=KE_final - KE_initial)...
What is the equation for work done by friction?
First find the strength of the friction force: f=uN=umg and multiply by displacement of magnitude d to get work done by friction: -fd=-umgd
What is the elastic potential of a compressed spring? How about KE?
Elastic potential energy = 0.5 k x^2 (where k is the spring constant)

KE=0.5 m v^2
What is the formula for gravitational potential energy?
mgh (h must be much less than the radius of the earth)
INFO: When adding momentums (to look at total before and after collisions), the velocities should reflect their directions.
On an incline, what is the work done by the normal force?
Zero since N is perpendicular to the displacement of the object.
What do you need to worry about when finding the work when raising an object?
Work should be negative because gravity is a downward force and this is being opposed by the object's displacement which is upward.
An object of mass 2 kg floats motionless in a fluid of specific gravity 0.8. What is the magnitude of teh buoyant force? (Use g=10m/s^2)
Since the object is motionless, its acceleration is clearly zero, so the net force on it must also be zero. Therefore the magnitude of the buoyant force upward must equal the magnitude of the weight downward: B=w=mg=20N.
What is specific gravity?
Tells us how dense something is compared to water.
specific gravity = density of substance / density of water
When dealing with stuff floating in water, what should first come to mind?
- Buoyant force upward must be balancing the weight downward.
- B = w = p V g (where density of water is 1000 kg/m^3)
A block of some unknown material is floating in a fluid of specific gravity 1.5. If one half of the block is submerged, what is its density?
For floating objects, the weight downward is balanced by the buoyant force upward. The density of the fluid is 1.5x the dnesity of water, that is p_fluid=1500 kg/m^3.

If half of the unknown material is submerged, than it its density is 750 kg/m^3.
An object is weighed in air and it is also weighed while totally submerged in water. If it weighs 100N less when submerged, find the volume of the object.
Reason why it weighs less is b/c there is 100N buoyant force pushing up.
100N = p_water V g
An object whose specific gravity is 2.0 weighs 200N less when it is weighed while totally submerged in water than when it is weighed in air. What is the weight of this object in air?
Find volume first. B=p V g => V = B/(p_fluid g)... here p_fluid is water so 1000
Once know V; can plut it into equation w=p V g = (2*1000)(V)(10).

Better way of doing it is just do:
w/B = Specific Gravity
A block of wood is in the shape of a cube with edge length 0.5m. When the top surface of this block is at a depth of 10m below teh surface of a body of water, the buoyant force it feels has magnitude F. When the top of the block rises to a depth of 5m, what is the magnitude of the buoyant force.
Since teh block is totally submerged at both depths, the buoyant force, B = p_water V g (called F in this question), is the same at both depths.
Archimede's Principle
The strength of teh buoyant force is equal to the weight of the fluid displaced by the object.
What is the formula for Hydrostatic Gauge Press? What are the units?
P_gauge=p_fluid g D
where p_fluid should be in pascals (1atm=100,000 Pa); D is the depth.
When dealing with P_total in terms of atmospheric pressure and gauge pressure?
P_total = Pgauge + P atm
What does repulsive force have to deal with? Does it have anything to do with mass?
Distance and charge; Has nothing to do with mass.
Is electrostatic field strength affected by the sign of a source charge?
- No, the sign of the source charge affects only the direction of the electrostatic field vectors;
- they will point away from the source charge if it is positive and toward the source charge if negative.
Does the nature of the medium surrounding the source of a charge dependent on the nature fo the medium surroudning the source charge?
Yes, ie. a source charge embedded in an insilator. The presence of the surroudnign insulating material will decrease the electrostatic field created by the charge.
What direction do field vectors point based on charge?
electric field vectors aways point toward negative source charges and away from positive charges.
What are the units fo an electric field?
An object with a mass of 1.25 kg and a charge of -1C is at rest 2m above a large positively-charged plate. The object experiences a constant electric field of 5 N/C. If the object is free to move, what will be its approximate velocity at the instant it strikes the plate?
W = F_elec d = q E d

Word done by the electric force is responsible for the increase in the object's KE.

So q E d = 0.5 m v^2
solve for v
An object with mass m and a net charge of -q moves in a circular orbit of radius r around a fixed object of mass m with a netcharge of +1. Neglecting any gravitational interaction, whcih one of the following expressions gives the speed of the orbiting object?
The attractive Coulomb force provides the centripetal force; that is, kq^2/r = mv^2/r. Solve for v.
Formula for force exerted on a point charge?
An object has a charge of -1 coulombs. How many excess electrons does it have?
q=n(-e) => n=q/(-e)
one electron is -1.6e-19C. Divide this by 1 and there are 6.25e18 electrons.
Calculate the magnitude of the electrostatic force btw two point charges, each of which has a deficit of ten billion (=10^10) electrons and which are separated by 1cm.
What is the formula for resistance in terms of resistivity?
R = p L / A
P10 pg 297: The charges, +Q and -2Q, aer fixed at a distance d to the left and right of the origin along the x axis as shown above. The potential infinitely far from the charges shown is equal to zero. Find the position on the xaxis closest to the origin where the potential is also zero.
The ratio of the distances from the charges to the zero potential position is 2:1. So 2/3 to the left of the origin in the direction of +Q.
What determines the speed of a wave?
- It is determined by the characteristics of the medium (and the tyep of wave).
How many cycles is a displacement from the position of maximum elongation to the position of maxmimum compression represent?
half a cycle.
What is the formula for the speed of a wave?
speed is equal to wavelength times frequency
(v = lambda x frequency)
Sound would be expected to travel most slwoly in a medium that exhibited...?
low resistance to compression and high density.
velocity = sqrt(B/p)
B=bulk modulus (resistance to compression)
What is the formual for the sound level (in dB) of a sound wave of intensity I? What does this only depend on?
B=10 log(I/I_o) where
I_o=10^-12 W/m^2.
- It only depends on I.
- Note: B is independent of v, lambda, or f.
The displacement of an object executing simple harmonic motion is expressed by the equation x=3cos(wt + pi/3) [t in seconds, x in cm]. At which of teh following positions x will the block have its greatest speeed?
The speed is the greatest when all the energy of the object is in kinetic form, which happens when then the potential energy is zero. THe position where this occurs is the equilibrium position, x=0.
What does simple harmonic motion imply?
The restoring force is proportional to the displacement, so the force is greatest when the displacement is greatest, and, since F=ma, this is also where teh acceleration is the greatest.
The displacement of an object executing simple harmonic motion is expressed by the equation x=3cos(wt+pi/3) [t in seconds, x in cm]. The acceleration of the block is the greatest at which of the following positions x?
The restoring force is proportional to the displacement, so the force is greatest when the displacement is greatest, and, since F=ma, this is also where teh acceleration is the greatest.

The given equation tells us tha tthe block oscillates btw x=-3 and +3 cm, so (one of the positions of) the greatest dispacement (=the amplitude) is at x=3cm.
Two transverse waves travel in the same direction along a stretched string. Individually, they share the same amplitude and requency. However, at t=0 where wave #1 has tis max positive displacement, Wave #2 has zero displacement; and where wave #1 has zero displacement, wave #2 has its max positive displacement. What is the phase different between them?
90 degrees.
What is the distance between an antinode and the nearest node for a standing wave?
1/4th the wavelength
Linear mass density
What is the distance btw any two adjacent nodes?
half a wavelength
Consecutuve harmonic wavelengths on a stretched string are 4m and 3.2m. How long is the string? (Note: Harmonic wavelengths lambda occur when L = n lambda / 2, where L is the length of the string and n=1,2,...)
Remember that when a standing wave is formed, the length of the rope must be a whole number half wavelengths, L=n(lambda/2). So should be divisible by 2 and 1.6.
A sound wave with frequency f travels through air at speed v. WIth what speed will a sound wave with frequency 4f travel through air?
Since the wave speed is independent of the frequency, the speed is still v. (Of course, the wave with frequency 4f will have 1/4 the wavelength, but the wave speed will stay the same.)
What is intensity defined as?
Average power delivered per unit area; I=P/A
WHen two tuning forks are struck simultaneously, beats are heard every 250ms. If one of these tuning forks produces a 498-Hz soudn wave, what could be the frqeuency of the sound wave produced by the other tuning fork?
498 +/- 4ms
A 2-m long organ pip, closed at oen end, is resonanting at its 5th harmonic. How many times greater is this resonant frequency than the fundamental resonant frequency?
Fifth harmonic freq is 5x the fundamental. (This is a general fact which you will find worthwhile to simply know. Whether the pipe is open or closed, teh nth harmonic frequency is n times the fundamental frequency.)
What is snell's law?
n_1 sin(theta_1) = n_2 sin(theta_2)
What is the refractive index of air?
- What condition must be present for TIR to be possible?
n2 > n1;
the angle of incidece must be large enough so that theta_1 = sin^-1(n2/n1)
If theta1<theta2, then how should n1 relate to n2?
If going into glass from air, how should the angle of refraction compare with that of incidence?
glass has higher n, so angle of refraction must be less and tehrefoer will tend to bend more towards the normal.
If the angle of incidence at the surface of the liquid is 0 deg, then what is the angle of refraction?
0 degrees as well. the refracted ray continues straight downward.
what is the mirror equation?
what is the magnification equation?
Mirror equation: 1/i + i/o = i/f
Magnification equation: m=-i/o
What is the conversion between atm, pascal, torr, mmHg?
1 atm = 101300 Pa = 760 torr = 760 mmHg
Intuition question: A piece of styrofoam and a gold brick are fplaced in a large tank which is then completely filled (to the brim) with water. The gold is carefully removed (no water is lost), and the water level decreases slightly. The goad is then placed on top of the styrofoam. If the styrofoam continues to float, then: a. the water level will rise, but not to the brim b. some water will spill out of the tank c. the water level will rise exactly to the brim and no water will spill from the tank. d. cannot be determined
since styrofoam is much less dense than gold, the volume of styrofoam pushed down into the water is much greater than the volume of the gold, so some water will spill out. V'_sub = V_sub + p_gold/p_water V_gold > V_sub + V_gold Vsub=(p_object/p_fluid) V
What is the ratio of the volume that's submerged to the object's volume?
V_sub / V = p_object / p_fluid
The open U-tube shown above (pg275 of science review book, #18) contains water and an oil of unknown density. GIven tha tthe distances x and y are 5cm and 20cm, respectively determine teh specific gravity of the oil.
p_water g y = p_oil g (x + y)
Flow rate equation
Gauge pressure equation - does it depend on V or shape of the container?
gauge pressure = fluid density x g x depth - no it doesn't depend on shape or V
Simplifying resistance of two resistors in parallel equation?
R = R_1 R_2 / (R_1 + R_2) 1/R = 1/R1 + 1/R2 + 1/Rn
What is the convention of electric flow?
By convention, the direction of electric current is the direction that positive charges would move. Therfore, current flwos from points of higher potential to points of lower potential.
Given a constant voltage, the addition of resistors in parallel to a resistor in an existing circuit will bring about?
The total resistance of a network of parallel resistors decreases as more resistors are added to the network. A decrease in the total resistance will result in an increase in the total current through the network.
Power equation
P = I V = I^2 R
If a circuit has the most resistance, does it consume the most/least amount of power?
Least because P=IV. I=V/R and if R is the greatest, then I will be the least => Power will be the least.
What is the formula for for electrical froce and gravitational force?
F_elec = k q1 q2 / r^2
F_grav = G m1 m2 / r^2
Right hand rule
thumb: velocity
fingers: magnetic field
palm: force
If you have a current flow and an electron projected, the direction of the magnetic force felt by the electron will be:
First find the magnetic field of the current. Then u need to use the magnetic field to find the magnetic force felt by the electron.
Right hand rule: proton/electron?
Left hand rule: proton/electron?
right hand rule: proton
left hand rule: electron
Rotation equilbirium signifies what?
net torque of zero.
How are rotaitonal equilibrium problems solved?
1. draw a diagram
2. write an expression for the net torque
3. set the net torque equal to zero and solve.
relationship btw centripetal force and frictional force for a car rounding a curve
If the centripetal force must be provided by friction alone on a curve, an increase in speed could lead to an unexpected skid if friction is insufficient.
What are the units of 1kW? What are the units of 1kWh? Is kWh a unit of power power or energy?
1kW = 1kJ/s
1kWh = 1kJh/s
1kWh is a unit of energy!
Energy (or work) divided by time