Originally Posted by sureshs
Conservation of momentum does not even apply here, because there is a net force being imparted to the racket.
Letís analyze collision of the resting ball with moving racquet.
The ball during impact stays on the racquet's string bed just about T = 4 msec. Assume, it leaves the racquet with speed equal to V
b=100 mph (160 km/h). The mass of the ball is m
b = 57 grams.
The ball kinetic energy before impact = 0.The ball kinetic energy after impact E
In physics, power is the rate at which energy is converted. Letís calculate power P
which produced the conversion of the ball kinetic energy from zero to E
It is P
Where, hp is horsepower.
The 20 horses are working very hard during 4 msec to provide the conversion of the ballís kinetic energy.
Should you apply during impact your own additional force to help them to do this work? Even if you add your maximum force during collision the result would be negligible. We have to collect kinetic energy during our forward swing. Thatís why there is no short swing in professional tennis when pros hit hard strokes.
So, when we scrutinize real collision of racquet and ball we can ignore the additional force completely!!!