Work, power, acceleration problem

[jehan4141]

A helicopter, starting from rest, accelerates straight up from the roof of a hospital. The lifting force does work in raising the helicopter. An 810-kg helicopter rises from rest to a speed of 7.0 m/s in a time of 3.5 s. During this time it climbs to a height of 8.2 m. What is the average power generated by the lifting force?

M = 810 kg
V₀ = 0 m/s
V_f = 7 m/s
t = 3.5 s
y = 8.2 m

Force acting on helicopter: mg and F_L (the lifting force)

It is accelerating upward. Find acceleration, a:

V_f = Vo + at
a = (V_f - Vo)/t
a = 2 m/s²

F_L - mg = ma
F_L = mg + ma
F_L = 810(9.8+2)
F_L = 9558 N

P = F_L x avg V = 9558 N x 3.5 m/s
P = 33453 watts?

 

[gneill]

Looks alright. You might want to express the result using the appropriate number of significant figures.

 

[jehan4141]

Thank you so much! My quiz is tomorrow and I wasn't sure how to do this type of problem!