# Homework Help: AS Physics Linear Momentum Question

1. Aug 2, 2011

### seiei

1. The problem statement, all variables and given/known data
A lorry of mass 20,000kg is travelling at 20.0m/s towards a car of mass 900kg travelling at 30m/s towards the lorry. What is the magnitude of the total momentum?

2. Relevant equations
m1u1+m2u2=p1
Not sure about any others :\

3. The attempt at a solution
The lorry has a momentum of 400,000Ns in the positive direction and the car has a momentum of 27000Ns in the negative direction but this is before impact. Not sure how to go about this, any help would be appreciated.

2. Aug 2, 2011

### tiny-tim

welcome to pf!

hi seiei! welcome to pf!

(try using the X2 icon just above the Reply box )
That's fine … what's worrying you about that?

The total https://www.physicsforums.com/library.php?do=view_item&itemid=53" is just the sum (400000 - 27000), and it's the same before as after the collision anyway …

momentum (and https://www.physicsforums.com/library.php?do=view_item&itemid=313")

Last edited by a moderator: Apr 26, 2017
3. Aug 2, 2011

### seiei

Re: welcome to pf!

Oh right, I'll remember that for next time :D! Yeah I thought the answer was 373kNs but the text book answer said 427kNs... I was getting kinda confused. Anyways, it's probably just an error in the answers so I'll tell my teacher about that, thanks for the help!

Last edited by a moderator: Apr 26, 2017