# sol16 - Because there are no non-conservative forces, the...

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PHYSICS 103 Chapter 7 -- HW # 16 Questions 32. If the ball is considered to be the system, only the mechanical energy is conserved. The ball’s kinetic energy, gravitational potential energy, and momentum all change with height. If the system consists of Earth and the ball, momentum is also conserved. 42. Assume that in the beginning the spring is compressed the maximum amount. At this time there is no kinetic energy and all of the mechanical energy is stored in the spring as elastic potential energy. As the spring pushes the puck away the elastic potential energy is continually transformed into kinetic energy. The kinetic energy reaches its maximum value when the spring returns to its relaxed length. From this point the kinetic energy is transformed back into elastic potential energy. When the spring is maximally stretched, the kinetic energy has dropped to zero and all of the mechanical energy is once again stored in the spring. The process repeats as the puck returns to the point of maximum compression.
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Unformatted text preview: Because there are no non-conservative forces, the total amount of mechanical energy remains constant. 52. We can answer this question by calculating the power exerted by each of them. For Valerie we have 1200 J ÷ 10 s = 120 watts, and for Brett we have 5000 J ÷ 50 s = 100 watts. Therefore, Valerie is more “powerful.” Exercise 20. Let’s choose the gravitational potential energy to be zero at the level of the sidewalk. a) ( 29 ( 29 ( 29 2 0.1kg 10 m s 5 m 5 J GPE mgh = = = b) zero, by our choice for the zero level. c) KE GPE ∆ + ∆ = ( 29 5 J 6 J 11 J f i KE GPE KE = - ∆ + = - -+ = Note that the answer to this part of the question does not depend on our choice for the zero of gravitational potential energy. The ball initially has 6 J of kinetic energy and it gains 5 J of kinetic energy as it falls. d) Because the initial kinetic energy is independent of direction, the answer to part c) would not change....
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## This document was uploaded on 10/29/2011 for the course PHSX 103 at MSU Bozeman.

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