A footballer kicks a ball directly towards a wall 10m away and walks after the ball in the same direction at a constant speed 2m/s. The ball starts at 4m/s, but decelerates at a constant rate of 0.5m/s^2. When it hits the wall it rebounds to travel away from the wall at the same speed with which it hit the wall. a) Find the time after initial kick when the ball returns to the footballer. b) what assumptions have been made in your answer?