Question

A disc of mass $2kg$ and diameter $2m$ is performing rotational motion. Find the work done, if the disc is rotating from $300rpm$ to $600rpm$.

• A. $1479J$
  
• B. $147.9J$
  
• C. $14.79J$
  
• D. $1.479J$
  

Answer 1

The correct option is A $1479J$

$I=\frac{m{R}^2}{2}=1kg/m^2{\omega }_i=\frac{300\times 2\pi }{60}=10\pi {\omega }_f=\frac{600\times 2\pi }{60}=20\pi \Delta KE=\frac{1}{2}I({\omega }_f{)}^2-\frac{1}{2}I({\omega }_i{)}^2=\frac{I}{2}\left(\right(20\pi {)}^2-\left(10\pi {)}^2\right)=2\times 300{\pi }^2=1480J$