Homework Help: physics

Posted by Blessig iliya on Wednesday, October 12, 2011 at 4:05pm.

A lift is used to carry boxes to the top floor of a hotel 20m high.A total weight of 100kg of boxes was caried up in 20second.If the useful output of the engine driving the lift mechanism is 1.2 kilowatt.calculate the efficiency of the engine of the lift mechanism.

physics - Henry, Thursday, October 13, 2011 at 9:01pm
Fb = mg = 100kg * 9.8N/kg = 980N. = Force of the boxes.

Po = Fb*d / t = 980 * 20 / 20 = 980W. =
Power output.

Eff. = (Po / Pi)* 100%,
Eff. = (980 / 1200) * 100% = 81.67%.

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