A uniform disc of mass `M` and radius `R` is released from the shown position . `PQ` is s tring , `OP` is a horizontal line , `O` is the centre of the disc and distance `OP` is `R//2`. The tension in the string just after the disc is released will be `:`

Options

A. `(Mg)/(2)`
B. `(Mg)/(3)`
C. `(2Mg)/(3)`
D. none of these

Answer

C

Explanation

`(C )`
Applying Newton's law on the centre of mass `O`
`Mg-T=ma {a=` acceleration of centre of mass `}`
`tau = I alpha`, about centre of mass
`T=(R)/(2)=(MR^(2))/(2).alpha`
Also `a=(R)/(2)alpha` from above equations `T=(2mg)/(3)`