d
(d) Time of fall \(=\) \(\sqrt {\frac{{2h}}{g}} \)\( = \sqrt {\frac{{2 \times 10}}{{1000}}} = \frac{1}{{\sqrt {50} }}\)
In this time number of oscillations are eight.
So time for \(1\) oscillation =\(\frac{1}{{8\sqrt {50} }}\)
Frequency \(=\) \(8\sqrt {50} \,Hz\) = 56\(Hz\)