# Work and kinetic energy

1. Feb 26, 2008

### shenwei1988

A helicopter is used to lift a 72.7 kg astronaut 16.9 m vertically out of the ocean by means of a cable. The astronaut rises with constant upward acceleration of magnitude 7.23 m/s2 until she reaches the helicopter.

a) How much work is done by the helicopter on the astronaut?

W=1/2MV^2=FS

first try: V^2=2as W=mas=8882.9949J wrong
second try: F=mg W=mgh=12052.8603J wrong

someone help me please, thank you so much!!

2. Feb 26, 2008

### XxBollWeevilx

First find the force required to lift the person. Then use work is force times displacement to find the work.

3. Feb 26, 2008

### shenwei1988

is the force mg ?

4. Feb 26, 2008

### Runelord

Use Newton's Second Law.

F = m*a

Force of helicopter - mass of astronaut * g = mass of astro * 7.23

Therefore the Force the helicopter must exert is 7.23 m + mg

Work = Force x Distance, so its just (7.23 m + mg) (16.9) Joules. Good luck!

5. Feb 26, 2008

### shenwei1988

yeah, i forgot to add the force of helicopter. thank you man!!