# Momentum in special relativity

1. Feb 10, 2013

### sapz

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

I added a question as an image, what is the right way to find the momentum?

2. Relevant equations

3. The attempt at a solution

#### Attached Files:

• ###### qrltvty.png
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2. Feb 10, 2013

### Simon Bridge

You use the energy-momentum relationship.

$E^2 = m^2c^4 + p^2c^2$

The kinetc energy is $K=(\gamma -1)mc^2$ and $E=\gamma mc^2$

3. Feb 10, 2013

### sapz

Im aware of that. However could you please address the question in the picture? Which way is wrong, and why?

4. Feb 11, 2013

### Simon Bridge

The pic includes the question "What is the momentum of the moving particle?"
You wanted to know the right way to go about it - I told you.

It seems I misunderstood.
Define "right way". (What makes you think there is a wrong way in there?)
The pic shows you how to solve for two contexts in relation to the center-of-mass.

Last edited: Feb 11, 2013