A uniform string of length $20\;m$ is suspended from a rigid support. A short wave pulse in introduced at its lowest end. It starts moving up the string. The time taken to reach the support is : (take $g=10\;ms^{-2})$

Question

$\begin{array}{1 1} (1) 2 \pi \sqrt 2 s \\ (2) 2s \\ (3) 2 \sqrt 2 s \\ (4) \sqrt 2 s \end{array}$