# Momentum and collisions

1. Oct 19, 2012

### shanewatson

if a hard sticky mud ball is trown on a wall it sticks to it
it is an inelastic collision
K.E. is not conserved
but here momentum is also not conserved because mud had an initial velocity
so initial momentum of mud + initial momentum of wall (that is 0) = initial momentum of mud
final momentum of mud (that is 0 or less than its initial momentum)+final momentum of wall= 0 or less than total initial momentum
please explain hiw momentum is conserved here??

2. Oct 19, 2012

### mikeph

The wall/mud combination does have a small final velocity. If the wall is attached to a planet, this velocity is tiny, since the mass is huge.

3. Oct 19, 2012

### Staff: Mentor

Momentum is conserved - but if the wall is attached to the ground, you have to consider the momentum of the whole earth, which changes at the impact. The mass of earth is huge, so you won't be able to measure it.

Edit: Too slow :(

4. Oct 19, 2012

### shanewatson

will the stiky mud also have a final velocity??

5. Oct 19, 2012

### Staff: Mentor

The same as the wall and earth, probably.