Answer
Choice B.
Work Step by Step
The value of $\gamma$ is $\frac{1}{\sqrt{1-v^{2}/c^{2}}}$.
The relativistic kinetic energy is $(\gamma-1)mc^2$.
Here, we are told that $(\gamma-1)mc^2=mc^2$, so we know that $\gamma= 2$.
Solve for v when $\gamma=\frac{1}{\sqrt{1-v^{2}/c^{2}}}=2.00$
$$v=c\sqrt{1-1/\gamma^2}=0.866c$$
$$v=0.866(300m/s) = 260 m/s$$
