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. 3 J
B. 20 kJ
C. 2 J
D. 1 J

Explanation

Work needed = change in kinetic energy Final KE =0
Initial `KE = (1)/(2) mv ^(2) + (1)/(2) 1 omega ^(2) = (3)/(4) mv ^(2) ({:(because 1 = (1)/(2) mr ^(2)), (and omega = (v)/(r)):})`
`= (3)/(4) xx 100 xx (20 xx 10 ^(-2)) ^(2) = 3 J`
`|Delta K E| = 3 J`