# Homework Help: Momentum Vs. Kinetic Energy

1. Jan 19, 2008

### winston2020

Could someone please explain the difference between these two? I understand that they're obviously different, but I can't figure out where each of them should be used.

For example, I need to calculate how much energy it would take to stop a speeding asteroid. I have it's mass, and velocity, but I don't know whether I should calculate Momentum or Kinetic energy.

2. Jan 19, 2008

### jdg812

If you are going to spend your energy to stop an asteroid, you are on wrong way. Try to find a way to GET energy from the asteroid.

3. Jan 19, 2008

### winston2020

Well, that would be a good idea, but I'm essentially trying to find out how much energy it has... :tongue:

4. Jan 19, 2008

### jdg812

First of all, it has KINETIC energy.
If it is close to the Sun or the Earth, it has POTENTIAL energy as well...

P.S.
If you indeed would stop the asteroid near the Earth, you would spend rest of your life and your money TO KEEP IT IN REST!

5. Jan 19, 2008

### winston2020

I understand that. I don't want to stop it. I'm going to use a series of blasts placed approximately 20 degrees to the back of the asteroid to divert it off course. But to calculate how far it will be diverted, I need to know how much energy it has in the forward direction. What I don't know, is if I should use E = 1/2mv^2 OR P=mv.

6. Jan 19, 2008

### jdg812

E = 1/2mv^2, this is energy, better use (mv^2)/2 to avoid misunderstanding

P=mv this is momentum

7. Jan 19, 2008

### winston2020

I know that too :p

What I need to know is in which sense they should be used. To figure out how much energy needs to be used to divert the asteroid, would I use momentum, or kinetic energy?

8. Jan 19, 2008

### jdg812

90 degrees would be better... less energy needed...

You may start with momentum of asteroid, then add 20% (or less, or more) in perpendicular direction... then calculate energy you spent...