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Ch2-H1-solutions

# Ch2-H1-solutions - louey(cal2859 Ch2-H1 florin(56930 This...

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louey (cal2859) – Ch2-H1 – florin – (56930) 1 This print-out should have 29 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0points A ball moves in the direction of the arrow labeled c in the following diagram. The ball is struck by a stick that briefly exerts a force on the ball in the direction of the arrow labeled e . Which arrow best describes the direction of Δ vectorp , the change in the ball’s momentum? a b c d e f g h 1. b 2. h 3. d 4. e correct 5. a 6. g 7. c 8. f Explanation: Recall the definition of impulse: Impulse = vector F net Δ t = Δ vectorp. Therefore, whatever direction the net force points in, that will be the direction of the change in the ball’s momentum. We are told that the force is in the direction of e , so that is the correct answer. 002 10.0points You observe three carts moving to the left. Cart A moves to the left at nearly constant speed. Cart B moves to the left, gradually speeding up. Cart C moves to the left, gradu- ally slowing down. Which cart or carts, if any, experience a net force to the left? Give all correct choices, with your answers separated by commas. A. Cart A B. Cart B C. Cart C D. None Correct answer: B. Explanation: Keep in mind what is meant by “net force.” The net force is the vector sum of all the forces acting on an object. A net leftward force would mean that all vertical (upward or downward) forces cancel, and that the forces acting toward the left are greater than those acting toward the right. We also know that a net force acting in some direction will cause an acceleration in that direction. Let’s examine each cart. Cart A is moving at nearly constant speed. In this case, there would be nearly zero net force acting on the cart, since it is not accelerating in any direc- tion. So A is not a correct answer. Cart B is accelerating toward the left, so it does appear that there is a net leftward force acting here. Finally, Cart C is slowing down as it moves to the left, so in this case the net force is actually to the right, since the acceleration is in that direction. So C is not correct either, meaning the only correct choice is B . 003(part1of3)10.0points A hockey puck is sliding along the ice with nearly constant momentum vectorp i = ( 10 , 0 , 4 ) kg · m / s when it is suddenly struck by a hockey stick with a force vector F = ( 0 , 0 , 1700 ) N

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louey (cal2859) – Ch2-H1 – florin – (56930) 2 that lasts for only 4 milliseconds (0 . 004 s). What is the final momentum vectorp f of the puck? Begin by finding just the x component, p f,x . Answer in kg · m / s. Correct answer: 10 kg · m / s. Explanation: This is a straightforward application of the momentum principle. Let the system be the puck, and assume the only significant interac- tion on the system is with the hockey stick.
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