# Collision of two masses

1. Jun 11, 2006

### chandran

i would like to discuss the following two scenarios

Scenario 1)Mass A(velocity>0) moves towards Mass B(velocity=) and hits it. The final velocity is derived from applying the momentum conservation principle.

2)Scenario 2) The scenario is same as in scenario 1) but a spring is included in front of mass B.

The above two problems are given in a physics web.

I want to understand what is the difference between 1) and 2)

2. Jun 11, 2006

### meemosewa

Although i am not possitive, i think this may help.

Scenerio A: Object A strikes Object B and energy is transfered. As a result, Object A transfers momentum to Object B, and Object B then moves.

Scenerio B: Object A strikes the spring, which in turn exerts force of Object B. When the spring is hit, some of the energy is absorbed by the spring, resulting in Object B moving, but going a shorter distance than in scenerio A.

In Scenerio A, Object A should remain not move after coming into contact with Object B (if they are the same size.)

In Scenerio B, depending on the springyness of the spring, Object A would either be shot away as a result of the reciprication produced by the spring. If not shot away, Object A may roll away depending on its mass.

Hope this helps!

3. Jun 11, 2006

### Staff: Mentor

If the two masses stick together after colliding (you didn't specify), this is an example of an inelastic collision. KE is not conserved.

Assuming no energy is lost in the spring, this would be an example of an elastic collision. KE of the masses is conserved (assuming the spring's mass can be neglected).

In both collisions momentum is conserved.