A proton in motion makes head on collision with an unknown particle at rest. If the collision is perfectly elastic and proton rebounds back with 4/9 of its initial kinetic energy after collision, the mass of unknown particle is

A proton in motion makes head on collision with an unknown particle at

1.	A proton in motion makes head on collision with an unknown particle at rest. If the collision is perfectly elastic and proton rebounds back with 4/9 of its initial kinetic energy after collision, the mass of unknown particle is
Answer» Equal to mass of proton TWICE the mass of proton 3 TIMES the mass of proton 5 times the mass of proton ANSWER :D