A disc of radius 2 m and mass 100 kg rolls on a horizontal floor . Its centre of mass has speed of 20 cm/s . How much work is needed to stop it ?

Options

A. 1 J
B. 3 J
C. 30 kJ
D. 2 J

Answer

B

Explanation

Required work done = `- (K_(f) - K_(i)) = 0 + K_(i) = K_(i)`
`= (1)/(2) I omega^(2) + (1)/(2) mv^(2) = (1)/(2) ((1)/(2) mR^(2)) omega^(2) + (1)/(2) mv^(2)`
`= (3)/(4) mv^(2) = (3)/(4) xx 100 xx (20 xx 10^(-2))^(2) = 3J`