Physics 2nd Semester Exam Review
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A tennis ball and a ball of clay of the same mass are thrown at the same speed towards a wall, which will
experience a larger impulse? Change in momentum? Tennis ball because it has a greater velocity change
and therefore a greater change in momentum and impulse
What are the units for momentum? Kg* m/s
In what types of collisions is momentum conserved? All types of collisions as long as it is a closed system
A bird hits the windshield of a moving car…. Which experienced more force? More impulse? Great
momentum change? Both the same for all
A stick of dynamite explodes into two pieces, one much more massive than the other…. What can be said
about the momentum change of each piece? They are equal
In what type of collisions are kinetic energy conserved? Only elastic and those don’t really happen in real
life
Object 1 has a mass, M and a speed, 2V. Object 2 has a mass of 2M and a speed of V. Which one has a
larger kinetic energy? Object 1 b/c the KE equation is KE = ½ mv2 and since the ‘v’ is squared it is more
‘valuable’
Do things that explode have the same total momentum before and after the explosion? Do they have the
same kinetic energy? Yes, No
Ft = mΔv
Impulse = Ft
Ft=mΔv
On object is moving circular motion at a constant speed….. what direction does its velocity vector point?
Tangent to the path. What direction does its acceleration vector point? Towards the center
Is the moon accelerating…. How so? Yes, it is in circular motion and therefore it has centripetal
acceleration
A mass on a string is getting swung around in a circle…. This string breaks…. Describe the path of the mass.
Follows a path that is tangent to the circular path
How far do you have to get away from the Earth to get beyond the pull of its gravity? You can’t…. gravity is
pervasive…. It goes on forever.
If you stood on a planet with 8 times as much mass as Earth and a radius that is twice as large, how much
stronger would the gravitational field be than Earth’s? 2x times larger
Why do astronauts feel weightless when they are in orbit? They are continuously falling, much like you
would in a falling elevator….. there is no normal force so you only feel weightless without actually being
weightless.
The fact that satellites (moons, comets, planets, etc.) follow elliptical orbits says what about their speed
through the duration of the orbit. That it changes, faster when close…. Slow when far away
What is the centripetal acceleration of an object moving at 20 m/s on a track of radius 100m? 4 m/s2
What is the gravitational force between two people each of mass 90 kg when they are standing 3.0 meters
apart. 4.004 x 10-7 N
You weight 1000N on the Earth’s surface, what would you weight if you were 3 times further away from the
center of the Earth? 1000/9= 111.1 N
How are frequency and period related? Inverses of each other . How are frequency and amplitude related?
Theyre not
If a guitar string has a fundamtental frequency of 200 Hz what would be the next 4 frequencies that could set
it into resonant vibration? 400 Hz, 600 Hz, 800 Hz, 1000 Hz
You throw a ball against a wall 50 times in one minute, what is the frequency of throwing? 50/60 = .83 hz
25) An object has a vibration of frequency 210 Hz. How many vibrations does it go through each minute? 210 x
60 = 1260 vibrations
26) What is the length of a simple pendulum that has a period of 1.5 seconds? .559 m
27) If both the mass and length of a simple pendulum are double, by what factor will the period change? Square
root of 2
28) A pendulum has a length of 13.0 meters, what would be the period of the pendulum? 7.23 sec
29) The distance between two waves crests is 20m and completes one cycle every 1.8 seconds. What is the
speed of the waves? 11.11 m
30) A wave has a speed of 400 km/hr and a wavelength of 450 km, what is the frequency of the waves in Hertz?
.0889 hz
31) A wave has a speed of 100 m/s and a period of 2.10 ms, what is its wavelength? .21 m
32) Five seconds after a flash of lightning a clap of thunder is heard…. How far away is the lightning? 5 x 343 =
1715 m (slightly more than 1 mile)
33) Compare a high pitch to the low pitch. Which has a higher frequency? Amplitude? Wavelength? Speed?
High pitch has higher frequency and a lower wavelength…. Amplitude and speed stay the same
34) You are twice as far away from a constant sound source as you were before…… by what factor has the
intensity of the sound changed? ¼ as intense
35) A pipe of length L is open at both ends…. What are the wavelengths of the three lowest pitched tones
produced by this pipe? 2L, L, 2L/3
36) Where are there nodes and antinodes for any harmonic in a pipe that is open at one end and closed at the
other? Node at the closed end….. antinode at the open end
37) Two tuning forks have frequencies of 224 and 234, what is the beat frequency when they are sounded
simultaneously? 10 Hz
38) As you move very rapidly towards a sound source what properties of the sound will change? Intensity,
loudness, and frequency
39) An object accelerates as it moves away from you….. what is going to be happening to the pitch of the
sound? Its going to be getting lower and lower
40) An organ pipe open at both ends has a length of .70 m, if the velocity of the sound is 340 m/s what is the
frequency of the second harmonic of the pipe? 485 hz
41) Why was General Relativity needed to complete Special Relativity? Special relativity only addressed
constant motion but left out acceleration and gravity….. this is what GR covered
42) How long does it take light/information from the sun to reach earth? About 8 minutes
43) What did the equivalence principle say about acceleration and gravity? Can you tell the difference between
the two? Gravity and acceleration are the same thing…. Cannot tell the difference between the effects of
gravity and the effects of acceleration
44) How does a black hole form? A large star runs out of nuclear fuel, this takes away the outward force inside
a star which leaves only gravity to take over. Gravity pulls inward and if the star is large enough it will
collapse to infinitely small
45) How does Einstein explain gravity? (in a few words, what is gravity according to Einstein) gravity is the
curvature of space-time around a massive object
46) How is it that a person could travel 100,000 light years of distance (according to stationary observers) in less
less than 100,000 years? (time dilation) time moves more slowly when you are going at a high rate of
speed… so since the travelers time is slowed down compared to Earth’s he can go through only a few years
while Earth would have to experience slightly more than 100,000 years.
47) A spaceship is travelling at 50% the speed of light and shines a beam of light out in front of it…. How fast
would a stationary observer measure the light to be moving? C ….. the speed of light….. all observers need
to see light moving at the speed of light