Hi, I was trying to figure whether a ball would have a larger exiting velocity if it started from rest or if it was coming towards me at a given velocity. My first thought is that it would have a greater exiting velocity if it started at rest. When I hit an incoming ball it will change direction and, since momentum is a vector, I believed the exiting speed would be smaller. I tried using some numbers from an old exercise question: 0.07 kg Ball Time of Contact between Ball and Tennis Racket: 0.1 second Maximum force exerted by Tennis Player 28 N Incoming Speed: -10 m/s The change in momentum the Tennis player can produce: F x Δt = 2.8 kgms (I set the incoming velocity as negative) 2.8 = 0.07v - (0.07 * (-10)) 2.8 = 0.07v + 0.7 v = 30 ms Now, if the ball started at rest: 2.8 = 0.07v - 0 v = 40 ms But if I set the incoming velocity as positive for example: 2.8 = (0.07 * -v) - 0.7 3.5 = (0.07 * -v) v = - 50 ms And this would change the whole thing! I am probably making a stupid mistake somewhere, I am confused Thanks, Peter G.