- The force on the ball hit by a golfer would be the change in momentum divided by the contact time.
- If it had an initial velocity, the force would be the final mv - initial mv, divided by the contact time.
- Car safety features are designed to lengthen the time in which the momentum changes. This reduces the force on the people on the car.
When a ball hits a wall and rebounds, its momentum changes, and providing there are no other forces, it will be equal but in the opposite direction.
Therefore the momentum has a minus sign in front of it.
It is the -mv-mu over time, but the velocities are the same so it is -mu-mu = -2mu.
If the ball doesn't hit straight on, the impulse is