In the triangle PQR, the hypotenuse is $1000$ and $\cos \;60^{\circ}= \large\frac{1}{2}$.<br> What is the length of the side PQ ?<br>

Question

$\begin{array}{1 1} (a)\;2000 \\ (b)\;500 \\ (c)\;1000 \sqrt 3 \\ (d)\;500 \sqrt 3 \end{array}$