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Homework Help: Another conservation of momentum

  1. Nov 5, 2006 #1
    The issue of the New York Times had a mass of 5.4 kg. Suppose a skateboarder picks up a copy of this issue to have a look at the comic pages while rolling backward on the sakteboard. Upon realizing that the New York Times doesn't have a "funnies" section, the skateboarder promptly throws the entire issue in a recycling container. The newspaper is thrown forward with a speed of 7.4m/s. When the skater throws the newspaper away, he rolls backwards at a speed of 1.4m/s. If the combined mass of the skateboarder and the skateboard is 50.0kg, what is the initial velocity of the skateboarder and newspaper?

    I don't know if it's asking for the combined Vi of the skateboarder and the newspaper or if it's asking for each. This is what I did though

    1. msvs,i + mnvn,i= msvs,f + mnvn,f = 50(vi+vi2)= (44.6)(-1.4)+(5.4)(7.4)
    2. 50(vi+vi2) = -22.48
    3. -22.48/50= -.4496

    I don't know if that's right, but I have no idea how to do it! help please!
  2. jcsd
  3. Nov 5, 2006 #2
    help please! =)
  4. Nov 5, 2006 #3
    is the skateboard frictionless?
  5. Nov 5, 2006 #4
    That looks about right. I am not sure about the math though. I trust you can check that yourself. It is not necessary to separate the initial velocities of the skateboarder and the newspaper like you did, since they are essentially the same thing. Thats what its asking really, don't get confused about it.

    It be really nice if you could clean up your equations in a more readable way though....
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