# Homework Help: Physics 12 Problem

1. Jun 28, 2005

### seiferseph

I have a quick physics 12 problem

A helicopter of 5500 kg starting from rest reaches a height of 5500 m with a velocity of 210 m/s. If this happens in 900 seconds, what is the Power?

i'm not sure how to do this one, i used P = W/t and solved for work being Ef - Ei. but is there no initial energy? so is it just

P = Ek + Ep (both final)/t
to solve? thanks!

Last edited: Jun 28, 2005
2. Jun 28, 2005

### dextercioby

You can assume that initially,the gravitatostatic potential energy is zero and that the gravity field doesn't vary significantly over those 5.5 Km,so you can set the gravitatostatic PE to "mgh".

Daniel.

3. Jun 28, 2005

### seiferseph

so can you solve like that for the power? Power = potential + kinetic / time ?

4. Jun 28, 2005

### Staff: Mentor

That's correct. (Assuming you measure the PE from ground level.)
$P = \Delta E_t /\Delta t$

5. Jun 28, 2005

### seiferseph

so potential is m*g*h with height being 5500, and kinetic is 1/2 m*v^2 with v being 210? thanks.

6. Jun 28, 2005

### dextercioby

Yep.The numbers are not too realistic,but it's okay so far.

Daniel.

7. Jun 28, 2005

### Staff: Mentor

That's right. (Realize that you are calculating the power required to raise the helicopter as stated in the given time; the actual power of the engine must be greater than that, since energy is wasted as thermal energy and air movement.)

8. Jun 28, 2005

### seiferseph

great, thanks!