Which of the following is not a perfectly inelastic collision?

The bob of a simple pendulum (mass $m$ and length $l$) is dropped from a horizontal position. It strikes a block of the same mass $m$ placed on a horizontal frictionless table. The collision is elastic. The kinetic energy of the block after the collision will be

In case of a perfectly elastic collision,

What happens when two identical bodies moving in opposite directions undergo a perfectly elastic collision?

During an elastic collision between two bodies,which of the following statements are correct?
$I$. The initial kinetic energy is equal to the final kinetic energy of the system.
$II$. The linear momentum is conserved.
$III$. The kinetic energy during $\Delta t$ (the collision time) is not conserved.

$A$ billiard ball moving with a speed of $5 \, m/s$ collides with an identical ball originally at rest. If the first ball stops after collision,then the second ball will move forward with a speed of ........... $m/s$.