Question

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

• A. 4 J
• B. 70 J
• C. 400 J
• D. 800 J

Answer 1

The correct option is C 400 J

$I=M{R}^2$(as it is similar to ring)

$=2\times (0.2{)}^2=0.08KE=\frac{1}{2}I{\omega }^2=\frac{1}{2}(0.08\left)\right(100{)}^2=400J$