a
(a) Coefficient of restitution or resilience of two bodies is defined as the constant ratio

of relative velocity after impact to the relative velocity of the bodies before impact

when the two bodies collide head on. There velocities are in the opposite directions.

Thus \(\frac{v_{1}-v_{2}}{u_{1}-u_{2}}=\) constant \(=-\mathrm{e}\)

The constant e is known as coeff. of restitution or resilience of two bodies.

For a perfectly elastic collision, \(\mathrm{e}=1\) and for a perfectly inelastic collision,

\(e=0 .\) Thus \(0 \leq e \leq 1\)