Conservation of Momentum (exam 3)

# Conservation of Momentum (exam 3) - Conservation of...

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Conservation of Momentum Concept Questions CTP-1 A car is sitting on the surface of the Earth and both the car and the Earth are at rest. (Pretend the Earth is not rotating or revolving around the Sun.) The car accelerates to a final velocity. After the car reaches its final velocity, the magnitude of the Earth's momentum is __________ the magnitude of the car's momentum. A) more than B) the same as C) less than D) Cannot answer the question because the answer depends on the interaction between the Earth and the car. Answer: the same as. The total momentum of the Earth/car system is zero. So if the car acquires a momentum to the right, the Earth must acquire an equal magnitude momentum to the left. |M E v E | = |m c v c |. Since M E >>m c , v E is incredibly tiny compared to v c , but v E is not zero. CTP-2 Suppose the entire population of Earth gathers in one location and, at a pre- arranged signal, everyone jumps up. About a second later, 6 billion people land back on the ground. After the people have landed, the Earth's momentum is.. A) the same as it was before the people jumped. B) different than it was before the people jumped. D) impossible to know whether the Earth's momentum changed.

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After the 6 billion people have passed the apex of their jump and are on the way down, the velocity of the Earth is.. A) away from the people B) toward the people C) zero Answers: Question 1) Same as it was before. The total momentum of the Earth/people system is zero. When the people are moving up(having just jumped), the Earth is recoiling away down. When the people are on the way back down, the Earth is moving up to meet them (due to the mutual gravitational attraction). When the people return to rest, so does the Earth. Question 2) toward the people. The people fall back toward the Earth because of the force of gravity, but the people exert an equal-sized gravitational attraction on the Earth as the Earth exerts on the people. So the Earth "falls" toward the people.
CTP-3 Two masses m 1 and m 2 are approaching each other on a frictionless table and collide. It is possible that, as a result of the collision, all of the kinetic energy of both masses is converted to heat. A) True B) False Answer: True. If the masses initially have equal and opposite momenta, so that the total

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