# Homework Help: Work, power, acceleration problem

1. Oct 13, 2011

### 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
Vf = 7 m/s
t = 3.5 s
y = 8.2 m

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

It is accelerating upward. Find acceleration, a:

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

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

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

Last edited: Oct 13, 2011
2. Oct 13, 2011

### Staff: Mentor

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

3. Oct 13, 2011

### jehan4141

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