Question

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

• A. $2100m/s^2$
• B. $1400m/s^2$
• C. $700m/s^2$
• D. $400m/s^2$

Answer 1

Answer: (A)

$2100m/s^2$

When dropped from the height $10m$ from rest, the velocity with which the ball hits the ground is

$u=\sqrt{2gh}=\sqrt{2\times 9.8\times 10}=\sqrt{196}=14m/s$ in vertically downward direction.

After the ball rebounds, it reaches maximum height of $2.5m$

so velocity just after the rebound is

$v=\sqrt{2\times 9.8\times 2.5}=\sqrt{49}=7m/s$ in vertically upward direction.

So average acceleration is $(7-(-14\left)\right)/0.01=2100m/s^2$ in vertically upward direction.