Question

An open tank containing non-viscous liquid to a height of
5 m is placed over the ground. A heavy spherical ball
falls from height 40 m over the ground in the tank.
Ignoring air resistance find the height to which ball will
go back. Collision between ball and bottom of tank is
perfectly elastic
(a) 45 m
(b) 35 m
(c) 40 m
(d) 20 m
​

Answer 1

The height to which ball will  go back if the Collision between ball and bottom of tank is  perfectly elastic is 40m

• In perfectly elastic collision, total energy will be conserved. That means no energy will be lost.
• The ball falls on the non viscous liquid and after collision it rises.
• Since liquid is non viscous , no work is done by the ball to travel through the liquid.
• That is it loses no energy while falling through the liquid.
• Since collision is perfectly elastic, no energy is lost while collision.
• Hence by applying conservation of energy, after the collision it should have sufficient kinetic energy to rise to the same height as it fell from.
• Therefore, it rises to 40m itself.