A basketball hits a wall at a speed of 20m.s-1 and leaves the wall at the same speed. At the moment when the ball's speed is momentarily zero, the ball is compressed by 0.3m. The mass of the ball is 0.5kg. Determine the force on the ball (exerted by the wall). Getting change in momentum is easy, but how do you get from there to the force? No time interval is given.