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A physical problem about pulleys
Solution: (1) The distance people move is s = vt = 0.5m/s *100s = 50m;

There are two ropes on the moving pulley, so the moving distance of the object is l =1/2s = 25m;

Friction f = 0.1g = 0.1* 600kg *10n/kg = 600n.

Useful work W=fL=600N*25m= 15000J.

(2)W total =W useful /75%= 15000J/75%=20000J.

W total =Fs F=W total /s=20000J/50m=400N.

(3)P=W total /t=20000J/ 100s=200w.

Answer: (1) People do useful work 15000J(2) People pull 400N(3) People pull 200w W.

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