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Homework 6-solutions

Homework 6-solutions - pels(kcp389 Homework 6 hill(666 This...

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pels (kcp389) – Homework 6 – hill – (666) 1 This print-out should have 31 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points A solid metal ball and a hollow plastic ball of the same external radius are released from rest in a large vacuum chamber. When each has fallen 1 m, they both have the same 1. kinetic energy. 2. momentum. 3. change in potential energy. 4. inertia. 5. speed. correct Explanation: All of the quantities mentioned above ex- cept terminal velocity depend upon mass. Note: If this experiment had not taken place in a vacuum chamber, none of these answers would have been correct. 002 (part 1 of 4) 10.0 points Calculate the momentum for a 0 . 2 kg rifle bullet traveling 600 m / s. Correct answer: 120 kg · m / s. Explanation: Let : m = 0 . 2 kg and v = 600 m / s . p = m v = (0 . 2 kg)(600 m / s) = 120 kg · m / s . 003 (part 2 of 4) 10.0 points What momentum does a 1200 kg automobile traveling 0 . 5 m / s (a few miles per hour) have? Correct answer: 600 kg · m / s. Explanation: Let : m = 1200 kg , and v = 0 . 5 m / s . p = (1200 kg)(0 . 5 m / s) = 600 kg · m / s . 004 (part 3 of 4) 10.0 points What momentum does a 90 kg person running 8 m / s (a fast sprint) have? Correct answer: 720 kg · m / s. Explanation: Let : m = 90 kg , and v = 8 m / s . p = (90 kg)(8 m / s) = 720 kg · m / s . 005 (part 4 of 4) 10.0 points What momentum does a 13000 kg truck trav- eling 0 . 02 m / s (a slow roll) have? Correct answer: 260 kg · m / s. Explanation: Let : m = 13000 kg , and v = 0 . 02 m / s . p = (13000 kg)(0 . 02 m / s) = 260 kg · m / s . 006 10.0 points What is the momentum of a two-particle sys- tem composed of a 1000 kg car moving east at 50 m / s and a second 1500 kg car moving west at 35 m / s? Let east be the positive direction. Correct answer: - 2500 kg · m / s.

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pels (kcp389) – Homework 6 – hill – (666) 2 Explanation: Let : m 1 = 1000 kg , v 1 = 50 m / s , m 2 = 1500 kg , and v 2 = 35 m / s . Thus p = m 1 v 1 + m 2 v 2 = (1000 kg)(50 m / s) + (1500 kg)( - 35 m / s) = - 2500 kg · m / s . 007 10.0 points A lunar vehicle is tested on Earth at a speed of 10 km/h. When it travels this fast on the moon, how does its momentum compare to the momen- tum on Earth? 1. None of these 2. the same as on Earth correct 3. less than on Earth 4. greater than on Earth Explanation: Its momentum is m · v . Because its mass and speed do not change, its momentum on the moon is the same as that on Earth. 008 10.0 points When an apple falls from a tree and strikes the ground without bouncing, what happens to its momentum? 1. The speed of the apple is equal and oppo- site to the speed of the Earth. 2. The momentum of the apple while falling is increasingly smaller. 3. The momentum of the apple after striking the ground is reversed. 4. The momentum of the falling apple is transferred to the Earth. correct Explanation: The momentum of the falling apple is trans- ferred to the Earth. When the apple is re- leased, the Earth and the apple move toward each other with equal and oppositely directed momenta. Because of the Earth’s enormous mass, its motion is imperceptible. When the apple and Earth hit each other, their mo- menta are brought to a halt – zero, the same value as before.
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