Question

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

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

Answer 1

Answer: (C)

20 J

Answer 2

We know that velocity at the top is $\sqrt{g r}$ and that at the bottom is $\sqrt{5 g r}$ Now difference in $K . E .=\frac{1}{2} m[5 g r-g r]=2 m g r$ $=2 \times 1 \times 10 \times 1$ $=20\, J$