Question

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

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

Answer 1

The correct option is C $400J$

Rotational Kinetic energy of a body $=\frac{1}{2}I{\omega }^2$

$I=M{R}^2$ for ring (mass concentrated on rim).

$I=2\times (0.2{)}^2=0.08kg{m}^2$

$\therefore E=\frac{1}{2}\times 0.08\times (100{)}^2=400J$