# Homework Help: Quick Momentum Question

1. Jun 16, 2010

### mcleodj2

1. The problem statement, all variables and given/known data

I'm given the masses of two objects, m1 and m2. The kinetic energy K is equal in both objects. It wants to know which object has the greater magnitude of momentum.

2. Relevant equations

K = 1/2mv^2 (Kinetic Energy)
p = mv (Momentum)
K = p^2/2m (K in terms of p)

3. The attempt at a solution

Now, I know that I have two variables to solve for before I can answer the question. I need to find v1 and v2. Finding one of those in terms of the other is easy, but that only leaves me with one equation and two variables. I can't for the life of me remember what relationship I can use to give me a second equation and my book isn't much help at all.
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Jun 16, 2010

### Mindscrape

Why don't you just equate the two

$$K_1 = K_2$$

$$\frac{p_{1}^2}{2m_1}=\frac{p_{2}^2}{2m_2}$$

Since you know the masses you just solve for one and see which one is greater. If p1^2=2p2^2 then p1 is obviously greater. :) You could take the square root too if you really wanted to get the right scale factor between the momentums.

3. Jun 17, 2010

### mcleodj2

Wow, do I feel stupid. You're right. I don't need an answer at all, just a ratio. I think I was blinded by a collision example done in class where the teacher did some sort of long problem where the solution wasn't immediately obvious. Thanks, Mindscrape.

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook