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Homework Help: Linear Momentum (One Dimension) Quiz Question

  1. Jul 15, 2010 #1
    Hello forum, today in my gr. 12 physics class I had a interesting question which I could not prove at all for the life of me. It is a really simple question, just with a little twist I suppose. As I was driving home from class I was thinking about what I was missing and thought up a solution. Anyways I'll state the question and all that jazz...

    1. Two people are sitting in a canoe which sits in the middle of a lake. Both individuals have a mass of 75kg, and the canoe itself has a mass of 50kg. The canoe is not moving, nor are the people sitting inside. Person 1 decides to throw to Person 2 a life jacket (edit: life jacket has a mass of 1kg) at 10m/s [E].

    Calculate the theoretical velocity of the canoe while the life jacket is still in mid air.


    Calculate the velocity of the canoe after person 2 catches the life jacket.

    Side note... the question was not worded at all like this, it was much more confusing! lol

    2. Relevant equations


    o=initial, f=final

    3. The attempt at a solution

    So here is my attempt at a solution,

    (a) (1kg)*(0m/s)+(200kg)*(0m/s)=(1kg)*(10m/s)+(200kg)*(X)
    X= -0.05m/s

    (b) (1kg)*(10m/s)+(200kg)*(-0.05m/s)=(1kg)*(0m/s)+(200kg)*(X)
    X= 0m/s

    ...So there it is. I was not to sure whether or not I should have combined the masses or not.

    Sorry for any typos, I just got home and am drained. Thanks for any help!
    Last edited: Jul 15, 2010
  2. jcsd
  3. Jul 15, 2010 #2


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    Hi LeonGrande and welcome to PF.

    Without the mass of the life jacket one cannot solve this. Looking at your solution, it is correct if the mass of the jacket is 1 kg. You seem to know what you're doing.
  4. Jul 15, 2010 #3
    Yeah, sorry, the mass of the jacket is 1kg... >_>

    Thanks for the quick reply! I guess I need to work on thinking clearly during tests/quizzes.
  5. Jul 15, 2010 #4


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    Then you are OK.
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