An important quantity to know during an inelastic is known as the coefficient of restitution, which essentially measures how "ellastic" a collision is. The coefficient of restitution, e, is defined as
e = ( v1,f - v2,f ) / ( v1,i - v2,i )
where the v's are speeds, not velocities. If a ball were to drop from a height of 5 m, and only bounce up to a height of 4 m, what is the coefficient of restitution for the collision between the ball and the floor?