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im_slow

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## Homework Statement

Massless Particles

A neutral pion traveling along the x-axis decays into two photons, one being ejected exactly forward and the other exactly backward. The first photon has three times the energy of the second. Prove that the original pion had speed 0.5c.

## Homework Equations

for m=0, E=p*c

conservation of Energy E^2=(c*p)^2+(m*c^2)^2

gamma=1/sqrt(1-Beta^2)

Beta = v/c

p=gamma*m*v

E=gamma*m*c^2

## The Attempt at a Solution

sum(momentum photons) = sum (momentum pion)