In another case it is accelerated in twice that time, eight seconds. The force required is reduced by one-quarter. This explains why there is a very critical speed at which an airplane will either fly or stall. The rate at which the air is pushed out of the way is squared . The difference in lift at fifty-six mph and sixty mph can be great.
Every action has an equal and opposite reaction.
As a bullet hits an animal, the force against the animal by the bullet is acknowledged. But the animal also exerts an equal force on the bullet. It is slowed down from very high velocity to zero velocity. A woodsman swings an ax at a tree. The ax exerts a force against the tree.