Question

A body of mass $1 \,kg$ is rotating in a vertical circle of radius $1\,m$. What will be the difference in its kinetic energy at the top and bottom of the circle? (take $g=10\,m{{s}^{-2}}$ )

• A. 10 J
• B. 20 J
• C. 30 J
• D. 50 J

Answer 1

Answer: (B)

20 J

Answer 2

Velocity at the top is $\sqrt{gr}$ and that at the bottom is $\sqrt{5gr}$ . Hence, required difference in kinetic energy $=\frac{1}{2}m[5gr-gr]=2gmr$ $=2\times 10\times 1\times 1=20\,J$