Find the velocity at which the kinetic energy of a particle equals its rest energy.

Explanation

`(m_0c^2)/(sqrt(1-v^2/c^2))=2m_0c^2`
or `sqrt(1-v^2/c^2)=1/2` or `1-v^2/c^2=1/4`
or `v/c=sqrt3/2`, i.e. `v=csqrt3/2`