# Relativistic Momentum of a photon

1.
An elementary particle of mass M completely absorbs a photon, after which its mass is 1.01M. (a) What was the energy of the incoming photon? (b) Why is that energy greater than 0.01Mc2?

## Homework Equations

p (photon) = E/c
p (particle) = γmv
p(i) = p(f)
Ek = γmc^2 -mc^2

## The Attempt at a Solution

I really have no idea where to start without having knowledge of the velocity of the particle after the collision

## Answers and Replies

mfb
Mentor
Just use v as velocity. Momentum conservation will give you that velocity during the calculations.

vela
Staff Emeritus
Homework Helper

## Homework Statement

An elementary particle of mass M completely absorbs a photon, after which its mass is 1.01M. (a) What was the energy of the incoming photon? (b) Why is that energy greater than 0.01Mc2?

## Homework Equations

p (photon) = E/c
p (particle) = γmv
p(i) = p(f)
Ek = γmc^2 -mc^2

## The Attempt at a Solution

I really have no idea where to start without having knowledge of the velocity of the particle after the collision
Was that the complete problem statement? I don't think the situation described is physically possible.

mfb
Mentor
It is possible, it is the reverse process of a gamma decay.

vela
Staff Emeritus
Homework Helper