Posted by Toung on Wednesday, December 19, 2012 at 4:47pm.
When a 51.7 gram tennis ball is served, it accelerates from rest to a speed of 41.2 m/s. The impact with the racket gives the ball a constant acceleration over a distance of 49.5 cm. What is the magnitude of the net force acting on the ball in newtons?

Physics  drwls, Wednesday, December 19, 2012 at 8:08pm
F = m*a
We first need to compute the acceleration, a.
V = sqrt(2aX)
41.2 = sqrt(2*a*0.495)
1697 = 2*a*0.495
a = 1714 m/s^2
F = m*a
= 0.0157 kg*1714 m/s^2
= 88.6 N
Another way to solve this is to equate the final kinetic energy to F*X (work done)
F = (1/2)MV^2/X
= (0.5)(0.0517)*41.2^2/(0.495)
= 88.6 N 
Physics  Toung, Wednesday, December 19, 2012 at 10:19pm
thank you so much