Question

A ball is dropped from a height of 10m. If $40\%$ of its energy is lost in collision with the earth then after collision the ball will rebound to a height of

• A. 10 m
• B. 8 m
• C. 4 m
• D. 6 m

Answer 1

The correct option is D 6 m

Initial kinetic energy, $\frac{1}{2}m{v}_1^2=mg{h}_1$
kinetic enrgy alter rebound = $\frac{1}{2}m{v}_2^2=0.6\frac{1}{2}m{v}_1^2=mg{h}_2$
$\frac{mg{h}_2}{mg{h}_1}=\frac{0.6\left[\frac{1}{2}m{v}_1^2\right]}{\frac{1}{2}m{v}_1^2}$
$\therefore h_2=0.6h_1=6m$