Question

When there is a kinetic energy loss then can we use the same formula for rebounding velocity

Answer 1

The coefficient of restitution (COR), also denoted by (e), is the ratio of the final to initial relative velocity between two objects after they collide. The value is almost always less than one due to initial translational kinetic energy being lost to rotational kinetic energy, plastic deformation, and heat. 

$$e=\frac{|\text{Relative velocity after collision}|}{|\text{Relative velocity before collision}|}$$