Question

A body falling from a height of 20m rebounds from hard floor. If it loses 20% energy in the impact, then coefficient of restitution is

• A. 0.89
• B. 0.56
• C. 0.23
• D. 0.18

Answer 1

Answer: (A)

0.89

Answer 2

It loses 20% energy in impact and only 80% energy remains with the ball

So ball will rise upto height

$h_{2} = 80\%\text{ of }h_{1} = \frac{80}{100} \times 20 = 16m$

Now coefficient of restitution $e = \sqrt{\frac{h_{2}}{h_{1}}}$

$= \sqrt{\frac{16}{20}} = \sqrt{0.8} = 0.89.$