Question

A spherical solid ball of a 1$kg$ mass and radius $3cm$ is rotating about an axis passing through its centre with an angular velocity of $50radian/s$. The kinetic energy of rotation is (in J)

• A. $4500$
  
• B. $90$
  
• C. $910$
  
• D. $\frac{9}{20}$
  

Answer 1

The correct option is D $\frac{9}{20}$

$MOI=\frac{2}{5}m{R}^2=\frac{2}{5}\left(1\right)(\frac{3}{100}{)}^2=\frac{2}{5}\times \frac{9}{{10}^4}=\frac{9}{25000}K.E=\frac{1}{2}I{\omega }^2=\frac{1}{2}\times \frac{9}{25000}\times {50}^2=\frac{9}{20}J$