As shown in the figure, a bob of mass m is tied by a massless string whose other end is wound on a fly wheel Ring of radius r and mass m. When released from rest the bob starts falling vertically. When it has covered a distance of h, the speed of the bob will be :

Options

A. `sqrt(2 gh)`
B. ` sqrt((2)/(3) gh)`
C. `sqrt(gh)`
D. `sqrt(1.5 gh)`

Answer

C

Explanation

`mgh = (1)/(2) (mr^(2)) ((v)/(r))^(2) + (1)/(2) mv^(2) , " " mgh = mv^(2) " " rArr " " v = sqrt(gh)`