Class 11 NEET Physics Motion in a Straight Line Questions

We know that when a ball is dropped from height h , it strikes the surface with speed
v=√2gh
It is given that the ball is dropped from height 5m . Substituting this value and value of acceleration due to gravity in the formula we get
v=√2×10×5 ,
v=√100 ,
v=10m∕s
We also know that when a ball rebounds with speed u , the height it reaches is given by H=‌

u2

2g

It is given that the ball reaches height 1.8m on rebound. Substituting this value and value of acceleration
due to gravity in the formula, we get 1.8=‌

u2

2×10

u2=36 ,
u=6m∕s
Hence the ball loses its velocity by 4m∕s on rebounding.
The fractional loss can be calculated by dividing the loss in velocity with initial velocity, i.e. velocity with
which it strikes the floor i.e 10m∕s
Hence, fractional loss in velocity =‌

4

10

, fractional loss in velocity =‌

2

5

.