Question

A wheel 2 kg having practically all the mass concentrated along the circumstance of a circle of radius 20 cm is rotating on its axis with angular velocity of 100 rad/s, then the rotational kinetic energy of wheel is ​

Answer 1

As we learnt in

Kinetic energy of rotation -

K=\frac{1}{2}Iw^{2}

- wherein

I = moment of inertia about axis of rotation

w = angular velocity

K_{rot}=\frac{1}{2}I \omega^{2}=\frac{1}{2}mr^{2}\omega^{2}

K_{rot}=\frac{1}{2}\times 2\times 400\times 10^{-4}\times100\times 100

K_{rot}=400J

Option 1)

4 J

This solution is incorrect

Option 2)

70 J

This solution is incorrect

Option 3)

400 J

This solution is correct

Option 4)

800 J

This solution is incorrect