The kinetic energy loss during a direct collision is important to be estimated in the cases when it is necessary to make a model of the actual collision between the ball and the tennis racket, because in actual conditions the latter is not stationary [22]. This can be determined using the following expression:
m1
u
E
=
k
−
k
=
1 2 1 2
2+2−2−2 (Eq. 11) this after being transformed becomes as follows:
Δ
E
=