Question

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

• A. $10m$
• B. $8m$
• C. $4m$
• D. $6m$

Answer 1

Answer: (D)

$6m$

Given that the ball is dropped from a height, $h_{=}10m$

Potential energy at $h_i=mg{h}_i$

Therefore, the potential energy at $h_i=m\times 10\times 10=100mJ$

On striking the ground level, the ball losses $40\%$ of its initial energy

That is,

$\frac{40}{100}\times 100mJ=40mJ$

The energy left on striking the ground $=100mJ-40mJ=60mJ$

So the final energy of the ball, $mg{h}_f=60mJ$

That is,

$h_f=\frac{60}{10}=6m$

Hence the ball will bounce back to a height of $6m$