Answer
$4.6\times10^{-19}kg \cdot m/s$
Work Step by Step
Find the momentum using equation 26–4.
$$p=\gamma mv=\frac{mv}{\sqrt{1-v^2/c^2}}$$
$$p=\frac{(1.67\times10^{-27}kg)(0.68)(3.00\times10^8m/s)}{\sqrt{1-0.68^2}}$$
$$p=4.6\times10^{-19}kg \cdot m/s$$