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pex2sm08 - August 4 2008 PHY 2053 Discussion Practice Exam...

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August 4, 2008 PHY 2053 Discussion Practice Exam 2 (Chapter 6-8) 1. A crane drops a 0.30 kg steel ball onto a steel plate. The ball’s speeds just before impact and after are 4.5 m/s and 4.2 m/s respectively. If the ball is in contact with the plate for 0.030 s, what is the magnitude of the average force that the ball exerts on the plate during impact? (Impulse-Momentum Theorem) a. 87 N b. 133 N c. 3.0 N d. 3.5 N 2. A machine gun is attached to a railroad flatcar that rolls with negligible friction. If the railroad car has a mass of 6.25 × 10 4 kg, how many bullets of mass 25 g would have to be fired at 250 m/s off the back to give the railroad car a forward velocity of 0.5 m/s? (Conservation of Momentum) a. 400 b. 2 000 c. 3 000 d. 5 000 3. In a two-body collision, if the kinetic energy of the system is conserved, then which of the following best describes the momentum after the collision? (Collisions) conserved 4. A 20-kg object sitting at rest is struck elastically in a head-on collision with a 10-kg object initially moving at +3.0 m/s. Find the final velocity of the 20-kg object after the collision. (Elastic Collisions)

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pex2sm08 - August 4 2008 PHY 2053 Discussion Practice Exam...

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