# Homework Help: Kinetic Energy

1. Jan 18, 2004

### celect

The question is:

If a sprinter running at 10 meters per second could convert his
kinetic energy into upward motion, how high could he jump?

How do I solve this if I use the KE = 1/2 mv^2

I dont know what the mass is?

2. Jan 18, 2004

### jamesrc

Imagine all of that kinetic energy converted into gravitational potential energy. If you solve for the height, I think you'll find that the mass of the sprinter cancels out.

3. Jan 18, 2004

### celect

So are you saying I should:

1/2 mv^2 = mgh
1/2 v^2/g=h
1/2(10^2/9.8)=5.1m

The text book I have in no way explains this, if this is correct
where can I get other sources of help on physics

4. Jan 18, 2004

### jamesrc

Yes, that's what I'm saying. I wouldn't expect your textbook to explain exactly the solution to this problem, especially if it is an exercise from there. As long as it explains about kinetic and potential energy, I wouldn't be too worried. The problem asks about an isolated "what-if" situation. What if instead of running at 10m/s, the sprinter jumped with an initial upward velocity of 10 m/s. I don't think there's anything more to read into the problem than that (which is why I don't think it's a problem if your textbook doesn't say anything about situations like this).

5. Jan 19, 2004

### celect

Thanks, I was searching for an answer that I would never find.