# Conservation of Energy (answer in Netwons)

1. Jan 26, 2012

### IBdoomed

Pam has a mass of 47.1 kg and she is at rest on
smooth, level, frictionless ice. Pam straps on
a rocket pack. The rocket supplies a constant
force for 15.3 m and Pam acquires a speed of
59.2 m/s.
What is the magnitude of the force?
The acceleration of gravity is 9.8 m/s^2

I know the KE= 1/2 mv^2 and that PE=mgh.
I do not know how to get an answer in newtons however..

2. Jan 26, 2012

### mukundpa

Do you know work energy theorem?

3. Jan 26, 2012

### Staff: Mentor

You also need the equation for work done by a force acting over a distance.

4. Jan 26, 2012

### IBdoomed

I do not! could you please explain?

5. Jan 26, 2012

### mukundpa

The theorem says in absence of any Resistance force increase in total energy of a body is equal to the work done on it. Here work is done by rocket pack force.

6. Jan 26, 2012

### IBdoomed

and work= power/time right? so how do i solve this if i don't know how long she was moving?

7. Jan 26, 2012

### mukundpa

Power is not involved at all.
work = force*displacement

8. Jan 26, 2012

### IBdoomed

oh sorry. well i'm pretty lost then... can you help me any more than this?

9. Jan 26, 2012

### mukundpa

work done = gain in PE + gain in KE

Last edited: Jan 26, 2012
10. Jan 26, 2012

### IBdoomed

I surrender.

11. Jan 26, 2012

### mukundpa

F*h = mgh + 1/2 mv^2 if it is going vertically
F*x = 1/2 mv^2 if it is moving horizontally