Conceptual Physics Exam Review Questions
Rotational/Circular Motion
1. What is center of gravity?
The average position of all of an objects weight…… in other words the center of an objects weight
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
What does center of gravity have to do with balancing?
support must be below the COG
Which will balance better, an object w/ a low COG or a high COG?
Low COG
Can an object have a COG that is outside of the actual object? (think of a donut)
Yes,….. donut, boomerang
What is torque?
A rotational push or pull…….. Force multiplied by lever arm (distance from axis)
What is it easier to open a door when you push on the side away from the hinge than on the same side as the hinge?
Larger lever arm means more torque
If you applied a torque to a meterstick that was balanced on a pivot what would happen?
It would rotate
If you have a meterstick that is balanced on a pivot, with weights on either side of the pivot…
a. …do the weights on either side have to be equal? No
b. …do the torques on either side have to be equal? Yes
Ice skater is spinning with arms and legs out, then pulls them in tight to their center? What happens? And Why?
Speeds up……. Skater reduced rotational inertia which means that the rotational speed must increase. Conserveration
of angular momentum says that this must happen.
Solid cylinder and hoop each of the same mass and radius roll down an incline…. Which will make it down the incline
faster? Why?
Cylinder because it has a lower rotational inertia bc its mass is more concentrated toward the center
A helicopter’s blades are rotating clockwise during a flight, if the tail rotor then breaks, what way will the body of the
helicopter rotate?
Counter clockwise
In order to balance, the total forces on both sides of an axis of rotation need to be equal.
False
Why will a non rotating bike wheel topple while a spinning wheel will stay upright?
Spinning wheel has angular momentum and since its magnitude and direction needs to be conserved it will maintain its
upright position. Bc of conservation of angular momentum spinning objects are much more stable and less likely to
topple
Why does a tightrope walker carry a long stick?
In increase his rotational inertia….. this makes him resist changes in his rotational state… in other words makes him more
balanced
Why do cats almost always land on their feet, even when they are dropped upside down?
The rotate their tails and their flexible body one way and their paws rotate the other…. This allows them to turn
around while still conserving their angular momentum
What is “Centripetal Force?
Center seeking force necessary for all circular motion
An object is being swung with a string in a horizontal circle, if the string breaks, what kind of path will the object take?
Tangent line path away from the circular path
A record is being spun about an axis going through its center, what point on the record has the greatest tangential
speed? Point on the edge What point has the greatest rotational speed? All the same
19. When a gymnast moves from an extended position to a tucked position, does she increase or decrease her rotational
inertia??
decrease
Gravity
20. What happens to gravity as you get further and further away from the center of the earth? It decreases by the inverse
square rule
21. If you were placed (perfectly at rest) 10,000 miles above the surface of the Earth what would happen to you? (float, fall
at 9.8m/s2, or fall at a rate lower than 9.8 m/s2)
22. Explain how satellites can orbit the Earth without ever crashing into the Earth.
Continuously fall around earth because their tangential speed is so high the rate that they fall matches the rate at
which the Earth curves away from it
23. What causes tides? (be specific) The difference in gravitational strength from the moon on the near side of the Earth
versus the far side
24. Newton said that the amount of gravity between two objects is directly proportional to their ___masses_______ and
inversely proportional to the square of the ____distance___________ between them.
25. If you could go to the center of the earth, would you feel really heavy or really light? Why? Really light…… as much
mass above as below you….. gravity in all directions would cancel out.
26. What type of path do the planets orbit the sun in? elliptical paths
27. If the Sun’s gravity all of the sudden magically shut off…. What would happen to the orbit of the Earth?
Fly away in a tangent line to its orbit
28. What is the inverse square of the number 3? 1/9
29. If you increased you distance away from the center of the earth by a factor of 3, by what factor would the force of gravity
th
acting on you change? Decrease by 1/9
30. What is the term meaning ‘irregularities caused in a planet’s orbit caused by its proximity to another planet’?
perturbations
31. If you placed two dice one inch apart in the middle of outer space (far away from any large planet or star), what would
happen to them? (Nothing, slowly get pulled together, rapidly get pulled together, or get pushed apart)
Relativity
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
What is the ‘opening’ of a black hole called? Event horizon
Is light fast enough to escape a black hole? No
How does General Relativity explain gravity? Gravity is the curvature of space-time around a massive body
What does special relativity say regarding time about objects moving at very high speeds? Fast clocks move slow
Explain time dilation. Two observers can experience different amount of time going by….. not everyo0ne needs to
experience time the same.
How could you possible age slower than everyone else? Travel at speeds close to the speed of light
Does the speed of light in a vacuum ever change? NO Can different observers see the speed of light to be different? NO
According to special relativity is there any difference between being at rest versus moving at a constant velocity? NO
What happens that makes a star collapse? Nuclear fuel runs out…. then gravity takes over
What three things can a star turn into after it collapses? White Dwarf, Neutron Star, Black Hole
What will the sun turn in to when it collapses? White Dwarf
If the sun all of the sudden magically turned in to a black hole, what would happen to the orbit of the Earth? Nothing
Which is denser a neutron star or a white dwarf? Neutron Star
Does a black hole have a ‘surface’? No
T or F…. Black holes are like cosmic vacuum cleaners that suck up everything and anything no matter how far objects are
away from it. False
Waves/Sound/Light
47.
48.
49.
50.
51.
What is the only thing that affects the speed of a wave? The medium that it travels through
Define wavelength. The distance between identical parts on consecutive waves
What is the period of a wave? The amount of time it takes for a full wave to pass by
What is the shortest wavelength of visible light? About 400 nm --- blue/violet light
What type of electromagnetic radiation has the highest energy? Gamma Rays Highest wavelength? Radio Waves
Highest frequency? Gamma Rays
52. How is light different than normal waves? Does not need a medium to travel through…. Energy associated with
frequency not amplitude.
53. What happens to the frequency of a sound wave as a sound source moves toward the observer? (Doppler effect)
It increases. High frequency on approach…… low frequency when receding
54. What is Doppler Effect? The perceived change in pitch of a sound because of the motion of the source relative to the
listener
55. If an ambulance is approaching you at a high rate of speed, will the pitch of the siren be higher or lower? Higher
56. Frequency is most closely associated with what property of a sound? (pitch, loudness, or intensity)
57. If the frequency of an object is 10 Hz what is its period? .1 sec
58. What type of wave is a sound wave? Longitudinal
59. What is the amplitude of a wave? The height of the wave above its equilibrium point
60. What is the difference between a longitudinal wave and a transverse wave? Longitudinal the medium vibrates parallel
to the direction of the wave….. transverse waves the medium vibrates perpendicular to the direction of the wave
61. What type of wave is a sound wave? Longitudinal
62. What is the part of a standing wave that doesn’t move called? Node
63. What is the part of a standing wave with maximum amplitude called? Antinode
64. What causes a tsunami? Underwater earthquake or landslide
65. What type of electromagnetic radiation is used for night vision and heat vision? infrared
66. What type of electromagnetic radiation is used for cell phone communication? microwaves
67. The region of expanded (decompressed) air in a sound wave is referred to by what name? rarefaction
68. What happens to wavelength of a wave when frequency is increased? decreases
69. What color will a beam of red light and blue light combine to form? magenta
70. If a Cyan colored light is shined on a yellow piece of paper in a dark room, what color will the paper appear? Green
71. If a Blue colored light is shined on a red piece of paper in a dark room, what color will the paper appear to be? Black
72. What are complementary colors? Two colors that will add together to produce white light