# Linear Momentum/System

Hey ya'll - I am not getting the kind of answers I need to be getting for this lab assignment!

Let's say that I am analyzing a car collision, and I have initial and final velocities (initial=before collision, final=after collision) and the masses of both cars. To calculate initial and final momentum of the system, do I just need to calculate individual momentum quantities for both cars? For instance, find initial and final P for each, and then use P(system)= m1v1 + m2v2...etc. for the i/f values??

In order to find total momentum, would I subtract final from initial?

(And just to be sure I am on the right page...finding momentum for each car is just mass*velocity...?)

Also...collision impulse is equal to the change in momentum...I take this to mean an absolute value quantity. Am I correct in my reasoning? Thank you so much for your time - any suggestions/advice will help. :)
Ciao,
Gin

## Answers and Replies

Is this a completely elastic collision? If it is, the TOTAL momentum of the system doesn't change no matter what. The total momentum is always the sum of each car's momentum.

In order to find total momentum, would I subtract final from initial?

that sounds like change in the momentum... although the law of conservation of momentum says the momentum at the beginning and the end stay the same...

so id say that the momentum at the beginning = momentum at the end

so m1vi1 + m2vi2 = m1vf1 + v2vf2

i think im right even though i havent done this in a while =P

oh yes if the collision isnt elastic then some momentum will be lost during the process... :X