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Homework Help: AS Physics Linear Momentum Question

  1. Aug 2, 2011 #1
    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
    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. jcsd
  3. Aug 2, 2011 #2


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    welcome to pf!

    hi seiei! welcome to pf! :smile:

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

    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
  4. Aug 2, 2011 #3
    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
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