# 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

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• ###### 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