Ch2-H4-solutions - chauhan(mmc2762 Ch2-H4 turner(56910 =...

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chauhan (mmc2762) – Ch2-H4 – turner – (56910) 1 This print-out should have 20 questions. Multiple-choice questions may continue on the next column or page – fnd all choices beFore answering. 001 10.0 points A tennis ball has a mass oF 0 . 059 kg. A proFes- sional tennis player hits the ball hard enough to give it a speed oF 51 m / s. The ball hits a wall and bounces back with almost the same speed. As indicated in the Following fgure, high-speed photography shows that the ball is crushed 2 cm at the instant when its speed iss momentarily zero, beFore rebounding. 2 cm vp i Making the very rough approximation that the large Force that the wall exerts on the ball is approximately constant during contact, determine the approximate magnitude oF this Force. Hint: Think about the approximate amount oF time it takes For the ball to come momentarily to rest. (±or comparison note that the gravitational Force on the ball is quite small, only about (0 . 059 kg)(9 . 8 N / kg) 0 . 6 N . A Force oF 5 N is approximately the same as a Force oF one pound.) Correct answer: 3836 . 47 N. Explanation: ±irst we want to fnd the time interval as the ball is slowing down during the collision. vV avg = i + f 2 V avg ,x = V i,x + V f,x 2 = 51 m / s + 0 2 = 25 . 5 m / s V avg ,x = Δ x Δ t Δ t = Δ x V avg ,x = 0 . 02 m 25 . 5 m / s = 0 . 000784314 s . Now apply the momentum principle. De- fne the system to be the tennis ball. The only signifcant Force on the ball during the colli- sion is due to the wall. Thus F net ,x = F wall ,x . | F net ,x | = v v v v Δ p x Δ t v v v v v v F wall ,x v v = v v v v p f,x p i,x Δ t v v v v = v v v v 0 (0 . 059 kg)(51 m / s) 0 . 000784314 s v v v v = 3836 . 47 N . 002 (part 1 of 9) 10.0 points A 0 . 7 kg block oF ice is sliding by you on a very slippery ²oor at 2 . 4 m / s. As it goes by, you give it a kick perpendicular to its path. Your Foot is in contact with the ice block For 0 . 003 s. The block eventually slides at an angle oF 23 From its original direction. The overhead view shows in the Following diagram is approximately to scale. The red arrow represents the average Force your toe applies brie²y to the block oF ice. II I III x z Which oF the possible paths shown in the diagram corresponds to the correct overhead view oF the block’s path?
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chauhan (mmc2762) – Ch2-H4 – turner – (56910) 2 1. I 2. II correct 3. III Explanation: Image II is correct because the kick is brief, and after the kick, vV is constant so the block will move with a constant velocity. 003 (part 2 of 9) 10.0 points Which components of the block’s momentum are changed by the impulse applied by your foot? (List all that apply, separated by com- mas. Remember that the diagram shows a top view, looking down on the xz plane.) Enter all choices that apply, separated by commas. A. The x component, p x B. The y component, p y C. The z component, p z D. None of the components change Correct answer: C.
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Ch2-H4-solutions - chauhan(mmc2762 Ch2-H4 turner(56910 =...

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