. If the impact is elastic, then the kinetic energy of the block after the collision is

A sphere of mass 0.1 kg is attached to a cord of 1m length. Starting from the height of its point of suspension this sphere hits a block of same mass at rest on a frictionless table

A. 1 J

B. 10 J

C. 0.1 J

D. 0.5 J

Best Answer

Ans: A

Sol: As two blocks are of same mass and the collision is perfectly elastic therefore their velocities gets interchanged i.e. the block A comes into rest and complete kinetic energy transferred to block B.

Now kinetic energy of block B after collision = Kinetic energy of block A before collision

= Potential energy of block A at the original height

= mgh = 0.1 ´ 10 ´ 1 = 1 J.