# What is the momentum (magnitude and direction )

• marisa29

## Homework Statement

1) A 4000kg freight car, moving at 4.0 m/s northwards, collides and couples with a 6000 kg freight car, which was initially at rest.
a) What is the momentum (magnitude and direction ) of the 4000 kg freight car before the collision?
b) What is the momentum of the two couples freight cars after the collision( magnitude and direction)
c) What is the common final speed of the two cars?
d) Extra credit consider the situation where the second (6000 kg) freight car was initially moving southwards at 2.0 m/s . After the collision the two freight cars couple together.

momentum=mxv

## The Attempt at a Solution

A) since before it hits would it just be 4000kg x 4.0 m/s = 16000 /NOrthwards
B) would we just add the two momentum so mv+mv and since the second it at rest would at just be 16000
C) m1v1+ m2v2/ m1+m2
so 1.6m/s

Yes, so p = m*v

m1v1 + m2v2 = 16000 like you said.

Now you equate 16000 = (m1 + m2)*v3 since now they are both together and have to move at the same speed. So you are right, you get 1.6m/s