An athlete doing bench presses in the weight room (which a physicist would proba

Question

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 95-kg barbell at constant speed. What is the athlete's average power output if he takes 2.2 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 during one lift How much work does gravity do on the barbell during the same lift?) A 230-kg piano rests on the ground. You want to get it into the back of a moving-truck 1.0 meter above the ground. You do NOT need to show your work for this problem. How much force would you (and your friends) need to exert on the piano if you lift it straight up through 1.0 m at constant speed? 230 N 1500 N 460 N 1900 N 720 N 2300 N How much force would you need to exert on the piano to push it up a frictionless 10 degree ramp to a final vertical height of 1.0 m at constant speed? (Your force is exerted parallel to the ramp.) 18 N 140 N 26 N 230 N 84 N 390 N What is the mechanical advantage of using the ramp in part (b), compared to lifting the piano straight up (Namely, what is the ratio of the two forces you calculated in parts (a) & (b)?) 3.2 7.5 4.0 9.0 5.8 10. How much work would you (and your friends) do on the piano by lifting it straight up in part (a)? 1500 J 5300 J 2300J 7800J 4400 J 8900 J How much work would you do on the piano by pushing it completely up the ramp in part (b)? 1500 J 5300 J 2300 J 7800 J 4400 J 8900 J Thought question [not for credit]: Would you expect your answers to parts (d) & (e) to be equal or different?

Explanation / Answer

(2) average power output of the athlete is = mgh/t

=95 x 0.70 x 9.8 / 2.2 Js-1

= 296.23 W ..............ans

(3) (a) F.2300N

(b) E.230N

(c) F.10

(d) B.2300J

(e) B.2300J

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