Q.

An object falls from a height of 10 m above the ground. After striking the ground it loses 50% of its kinetic energy. The height upto which the object can rebounce from the ground is:              [2024]
 

1 7.5 m  
2 10 m  
3 2.5 m  
4 5 m  

Ans.

(4)

Given, height (h)=10m

P.E. at h=10m, P.E.=mg×10=10mg

Before striking ground,

(K.E.)i=P.E. at h=10 m=10mg

After striking ground,

(K.E.)f=50%(K.E.)i=12×10mg

(K.E.)f=5mg

When object rebounces to h',

(K.E.)f=P.E. at h'

So, 5mg=mgh'  h'=5m