Question

If a sphere of mass $2kg$ and diameter $10cm$ is rolling at speed of $5m{s}^{-1}$. Its rotational kinetic energy is:

• A. $10J$
• B. $30J$
• C. $50J$
• D. $70J$

Answer 1

The correct option is A $10J$

$KR=\frac{1}{2}I{\omega }^2(V=R\omega )$

$=\frac{1}{2}(\frac{2}{5}\times 2\times R^2){\omega }^2$

$=\frac{2}{5}\times V^2$

$=\frac{2}{5}\times 25$

$=10J.$