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. 30 kJ
C. 2 J
D. 1 J

Answer

A

Explanation

We know that work done is equal to change in kinetic energy of system.
Final KE=0
Initial `KE=(1)/(2)mv^(2)+(1)/(2)lomega^(2)=(3)/(4)mv^(2)`
`=(3)/(4)xx100xx(20xx10^(-2))^(2)=3J`
`|DeltaKE|=3J`
Hence option (a) is correct.