# Momentum conservation

Tags:
1. Feb 22, 2015

### Joe Armas

1. The problem statement, all variables and given/known data
In the pictures

2. Relevant equations

Fnet = dp/dt

3. The attempt at a solution

I know in part b there is a net external force (gravity) that does positive work, fnet > 0, thus dp/dt is positive. Does the spring in part c increase or decrease the momentum of the system? I am not too sure of

2. Feb 22, 2015

### brainpushups

What is 'the system?' Is it both blocks or one block? Do you see how the answer is different in either case?

3. Feb 22, 2015

### Joe Armas

The system consists of the two gliders. So it appears that the spring is indeed an external force. But the direction the spring accelerates the block is in negative direction, so I am not sure how the TOTAL momentum of the system will change.

4. Feb 23, 2015

### haruspex

Even if you count the spring as external to the system (and I'm not sure that's intended), you are not given any mass for it. Taking its mass as zero, it cannot add or remove any momentum from the system of gliders.