A helicopter, starting from rest, accelerates straight up from the roof of a hospital. The lifting force does work in raising the helicopter. An 790-kg helicopter rises from rest to a speed of 7.0 m/s in a time of 3.0 s. During this time it climbs to a height of 7.2 m. What is the average power generated by the lifting force?

25032.47 W

Explanation:

Power is the time rate of doing work, hence,

P = Work done (non conservative) / time

Work done (non conservative) is given as:

W = total K. E. + total P. E.

Total K. E. = 0.5mv² - 0.5mu²

Where v (final velocity) = 7.0m/s, u (initial velocity) = 0m/s

Total P. E. = mgh (f) - mgh (i)

Where h (f) (final height) = 7.2m, h (i) (initial height) = 0 m

=> W = 0.5mv² - mgh (f)

P = [0.5mv² - mgh (f) ] / t

P = [ (0.5*790*7²) - (790*9.8*7.2) ] / 3

P = (19355 + 55742.4) / 3 = 75097.4/3

P = 25032.47 W