Here is the problem, and I'm banging my head against a wall trying to set it up: An athlete catches a ball traveling at 20 m/s with her hands. Between the time she makes contact with the ball and the time the ball stops moving, the ball travels a distance of 20 cm. The goaltender feels a force of 500 N against her hands when she stops the ball. What is the mass in kg of the ball? I know I need to find the acceleration here, and I started with a = (v-v0)/t. v0 =20 m/s, however I'm stuck on how to get v. I understand there is a huge deceleration going on from when the ball hits her hands to when it stops. I tried doing v=distance/time, so v=0.20m/t, then plugging this in for a, but this seemed to get way too complicated, where a=(.2m/t - 20)*1/t...I think I'm not on the right track here. Other equations needing to be used of course are ΣF=ma, but there again I circle back to the acceleration. Also, do I need to take gravity into consideration here, or do I need to break this into scalar x/y components? But if so I don't have an angle to work with, only the 20 m/s. I'm just looking for guidance in how to set up this problem. Any help is appreciated. Thank you!