# Greater change in momentum between two objects

1. Oct 21, 2005

### positron

When two objects collide, how do you determine which object experiences the greater change in momentum? for instance, if A and B with different masses travelling at different speeds collide, do they experience the same momentum change after the collision? What about KE?

This is my reasoning so far:
The change in momentum does not change, because the same force acts on both A and B for the same amount of time during the collision. However, the kinetic change because the masses of the objects are different even though the change in velocities are the same. Is this correct?

Last edited: Oct 21, 2005
2. Oct 21, 2005

### Diane_

You've correctly noted that the same force is acting on both A and B. It will obviously also act for the same amount of time, meaning the impulse imparted to each will be the same, give or take a direction. What is impulse, and what does this tell you about the momentum change for each block? And, if their masses are different, what does this tell you about the velocity change for each block?

Once you have that, consider that kinetic energy is linear in mass but quadratic in speed - what does that tell you about the change in kinetic energy for each block? It might be a good time here to write a few equations and calculate the ratios of the kinetic energy for each block before and after the collision. What do those ratios depend on?

Bottom line: You're making a couple of bad assumptions, but apart from those your reasoning isn't bad. Go back and look at the definition and defining equations for impulse, momentum and kinetic energy.