A weightless rigid rod with a small iron bob at the end is hinged at point A to the wall so that it can rotate in all directions. The rod is kept in the horizontal position by a vertical inextensible string of length `20cm`, fixed at its midpoint. The bob is displaced slightly perpenducular to the plane of the rod and string. Find period of small oscillations of the system in the form `(piX)/(10)s` and fill the value of X.

Explanation

The bob will execute SHM about a stationary axis passing through AB. If its effective length is l' then `T=2pisqrt((l')/(g'))`
`l'=l//sin theta=sqrt(2)l ` (because `theta=45`)
`g'= g cos theta=g//sqrt(2)`
`T=2pisqrt((2l)/g)=2pisqrt((2xx0.2)/10)=(2pi)/5 s`