2. (4 pts.) An athlete doing bench presses in the weight room (which a physicist
ID: 2030254 • Letter: 2
Question
2. (4 pts.) An athlete doing bench presses in the weight room (which a physicist would probably rename the “mass room”) applies a force straight up that is just enough to lift a 125-kg barbell at constant speed. What is the athlete’s average power output if he takes 2.7 s to raise the barbell straight up through a distance of 0.70 m? Show your work. (Thought question [not for credit]: How much work does the athlete perform on the barbell during one lift? How much work does gravity do on the barbell during the same lift?)
Explanation / Answer
Work done = m g h
= 125 x 9.8 x 0.70
W = 857.5 J
and t = 2.7 s
P = W / t = 318 Watt
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