work output = m g h = 100 * 9.81 * 20 = 19,620 Joules
watts = 19,620 J / 20 s = 981 watts = 0.981 kw
(0.981 / 1.2) * 100 = 81.8 %
a lift is used to Carry boxes to the top floor of a hotel 20m high.
A total weight of 100kg of boxes was carried up in 20sec .if the useful output of the engine driving the lift mechanism is 1.2kilowatt calculate the efficiency of the lift mechanism.
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