Question

A ball is is dropped on the floor from a height of $10m$. It rebounds to a height of $2.5m$. If the ball is in contact with the floor for $0.01s$, the average acceleration during contact is

• A. $2100m/s^2$ downwards
• B. $2100m/s^2$ upwards
• C. $1400m/s^2$
• D. $700m/s^2$

Answer 1

The correct option is B $2100m/s^2$ upwards

Velocity of ball at the time of striking the floor,
$u=\sqrt{\left(2g{h}_1\right)}=\sqrt{(2\times 9.8\times 10)}$
$=14m/s$ (downwards)
Velocity with which it rebounds,
$v=\sqrt{\left(2g{h}_2\right)}=\sqrt{(2\times 9.8\times 2.5)}$
$=7m/s$ (upwards)
Average Acceleration during contact is
$a=\frac{v-u}{t_2-t_1}=\frac{7-(-14)}{0.01}$
$=\frac{21}{0.01}=2100m/s^2$ upwards
(Taking upward as positive and downward as negative )