# If two objects collide and one is initially at rest, is it possible for both to be at rest after the collision?

I know that the straight answer to my question is no. Since the initial momentum is not zero, the final momentum is not zero.

What about when object A impacts object B that is rigidly fixed to earth and object B is very ductile, in the sense that it can endure without breaking considerable deformations. Let's assume that this ductility is enough to dissipate the energy transferred by the colliding object A and that object B is long enough so that only a fraction of its length will actually deform (move) during the impact of object A. Let's also assume that the impact prolongs over a time period that is larger than the time it takes for the impact waves to go through both objects so that all the mass is excited and involved in the impact itself.

My questions are:

1. How to apply momentum conservation to cases where one object comes to rest after collapse and part of the other object also?
2. Is momentum conservation applicable during the time period when the impact is taking place?
• Are you asking if something thrown can stick to the ground?
– Dan
Commented Mar 3, 2022 at 4:42
• No that's simple case. My questions are given above. Consider as an example the airbag. How to calculate the speed during impact? Commented Mar 3, 2022 at 8:23

For example, a bullet hits a wooden target and rests there. Its momentum $$p$$ disapeared. But when the shot was done, if we assume a rigid support for the rifle, the momentum $$p$$ cames from nothing.