A tennis ball crossing a net at 35m/s [S10 degrees W] strikes a person's racket and her volley returns it at 30m/s [N 30 degrees W]. If the person's racket was in contact with the ball for 0.005s then what is acceleration of the ball? For this question is my vi=35m/s and vf=30m/s? If so, when I draw my vectors do I subtract them or add them. The equation for acceleration is a=vf-vi/t right? Please help and post your final answer and solution as I need to compare with mine!