A uniform disc of mass m and radius r is suspended through a wire attached to its Centre. If the time period of the torsional oscillations be T, what is the torsional constant of the wire?

Answer

B

Explanation

M.I. of the centre of the disc `=(mr^2)/2`

`T=2pisqrt(I/K)=2pi sqrt((mr^2)/(2K))`
[where K=Torsional constant]
`T^2=4pi^2(mr^2)/(2K)=2pi^2(mr^2)/K`
`rarr 2pi^2mr^2=KT`
`rarr K=(2mr^2pi^2)/T^2`
. torsional constant
`K=(2pi^2mr^2)/T^2`