# Physics

A helicopter winches up an injured person from a boat. The person plus equipment has a mass of 104 kg. If the height of the lift is 84 m and it is carried out at a uniform rate over 70 s, what is the power expended by the helicopter's winch motor? Assume that the engine is 61% efficient.

1. Since the load moves at a constant speed the force applied by the engine is equal to the gravity force. Therefore, the work is
W=F•h = m•g•h.
Effective output is
P = W/t= m•g•h/t
Power of the engine is P/0.61 = m•g•h/0.61• t=
104•9.8•84/0.61•70=2005 W =2.005 kW

posted by Elena

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