Gymnasts often practice on foam floors, which increase the collision time when a gymnast falls. what effect does this have on collisions? the change in momentum needed to stop the gymnast is increased. the change in momentum needed to stop the gymnast is decreased. the force exerted by the floor on the gymnast decreases. the force exerted by the floor on the gymnast increases.

The force exerted by the floor on the gymnast decreases.  

Explanation:

Gymnasts practice on foam floors. This reduces their injury. If a gymnast falls, the collision time increases. Since the change in momentum is constant, the impulse would be constant. For change in momentum to remain constant, the force exerted by the floor would decrease.

Impulse, I = f × t = Δp = constant.

Thus, as the time of the collision increases, the gymnasts have less impact.

answer; i believe the answer is hydraulic action;