The frequency of oscillation in rad/sec of a simple pendulum of length l suspended inside a rocket moving vertically with an acceleration 'a' just above the earth is:

Question

$\begin{array}{1 1}(a)\;0 \\(b)\;\sqrt {\frac{(a+g)}{I}} \\( c)\;\sqrt {\frac{(g-a)}{I}} \\(d)\; \sqrt {\frac{(a-g)}{I}} \end{array}$