A helicopter, starting from rest, accelerates straight up fromthe roof of a hosp

Question

A helicopter, starting from rest, accelerates straight up fromthe roof of a hospital. The lifting force does work in raising thehelicopter. An 710-kg helicopter rises from rest to a speed of7.0 m/s in a time of 4.5 s. During thistime it climbs to a height of 9.5 m. What is theaverage power generated by the lifting force?

Explanation / Answer

The acceleration of the helicopter is               v = u + a t        ==> a = v /t = 7.0 /4.5 = 1.56 m/s2 The force experienced by helicopter is F = m a = 710*1.56 = 1107.6 N Therefore the lifting force   L = mg- F =710*9.8 - 1107.6 = 5850.4 N Therefore              Average power generated by the lifting force                                          P = W / t                                             = L.s / t                                             =5850.4 * 9.5 / 4.5                                             = 12350.844 W

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