When a photon bounce off an electron, it gives some of its energy to the electron. The photon has no mass, however, and it must continue to travel at speed c. How is its reduced energy manifested?

Answer 1

A 5kg fish swimming at 1 m/s swallows an absent minded 1-kg fish swimming toward it at a velocity that brings both fish to a halt. Find the speed of the smaller fish before lunch.

Answer 2

Since the post-lunch momentum is zero, the momentum of larger fish should be equal to the momentum of smaller fish in terms of magnitude but opposite in direction.
Speed of the smaller fish v2:
v2 = (m1*v1)/m2
= 5*1/1 = 5m/s

Answer 3

The photon loses momentum by reducing its frequency. the process is called Compton scattering.