How to make physics problem obey momentum conservation?

[toesockshoe]

Homework Statement

Can you change the system (as you would in a work/energy problem) so you can get rid of all external forces in a momentum problem for example by making your system the earth, a mass, and a spring (if the problem involved those 3 objects)?

Homework Equations

P=mv[/B]

The Attempt at a Solution

conceptual question

 

[Dale]

Even with a conceptual question you still need to show your own effort.

 

[toesockshoe]

But it's just a yes or no question.