Here's what the impact force looks like. (I should point out that I used a spring bumper during the collision to increase the impact time, so that we could more easily see how the force changes.) ...

A squash ball of mass 25 g is moving from left to right at 3.2 ms-1. It is hit by a squash racquet which applies a force for 4 milliseconds, so that the ball leaves the racquet at 8.4 ms-1 moving ...

the momentum after the collision is zero. In physics, this type of event is termed an explosion. Watch this video for a practical demonstration of conservation of momentum in explosions.