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33620_exam2_solutions

# 33620_exam2_solutions - Physics 160-02 Exam#2 Name_Box 1 I...

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Physics 160-02 Exam #2 Name:___________________Box #_________ 1) I throw a 0.5kg ball straight up with an initial velocity of 5m/s. The ball goes to its maximum height, stops and comes back down to the point at which I it left my hand. During its round trip, air resistance takes out 4J of energy. What is its speed when it returns to my hand? From conservation of energy, the net change in total energy is zero, so when it returns to my hand (where the change in gravitational energy is zero) the change in kinetic energy must be equal to the loss from air resistance: 2 2 2 2 0 1/ 2 1/ 2 1/ 2(0.5 )(5 / ) 4 1/ 2 6.25 4 2.25 3.0 / tot th f i th f f E K E mv mv E kg m s J mv J J J v m s

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As the figure below shows, a 10kg block is accelerated by a compressed spring whose spring constant is 4 00N/m. After leaving the spring at the spring’s re laxed length (0m), the block travels over a horizontal surface with a coefficient of kinetic friction of 0.2, for a distance of 4m before stopping (the floor is frictionless to the left of 0m). 2) What is the increase in the thermal energy of the block-floor system? 3) What is the maximum speed of the block? 4) Through what distance is the spring compressed before the block begins to move?
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