Question

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 ?

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

Answer 1

The correct option is A $3J$

We know,

Work required = change in kinetic energy

Here, Final $KE=0$

So Initial $KE=\frac{1}{2}m{v}^2+\frac{1}{2}I{\omega }^2=\frac{3}{4}m{v}^2$

$=\frac{3}{4}\times 100\times (20\times {10}^{-2}{)}^2=3J$

$⟹|\Delta KE|=3J$

Hence option A is correct answer