A disc of radius 2 m and mass 100kg 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. 1J
B. 3J
C. 30kJ
D. 2J

Answer

B

Explanation

Work done `= Delta KE`
`(KE)_(i) = (1)/(2) I omega^(2) + (1)/(2) mv^(2)= (3)/(4) mv^(2)`
`= (3)/(4) xx 100 xx (20 xx 10^(-2))^(2)= (3)/(4) xx 100 xx 400 xx 10^(-4) = 3J`