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Homework Help: Velocity / Momentum Questions

  1. Sep 7, 2007 #1
    1. The problem statement, all variables and given/known data

    I have three questions:

    1. "The car rounded the corner at a constant velocity." Would this statement make sense to a physicist?

    2. A cup sitting on a table constantly receives upward momentum from the table, T or F?

    3. Imagine that a 1.0 kg cart traveling rightward at 1.0 m/s hits a 3.0 kg cart at rest. Afterward, the smaller cart is observed to move leftward with a speed of 0.75 m/s. What impulse did the collision give the smaller cart at the expense of the larger?

    2. Relevant equations

    None

    3. The attempt at a solution

    1. No, the word velocity is being used incorrectly.
    2. I don't know about this one. I would say true, if the compression contact interaction of the table can be considered as velocity (which is a component of momentum). False, if the table is not displacing anything, hence there is no displacement over time or velocity.
    3. I don't understand the question. The collision gave the smaller car an impulse? Well, I suppose 0.75 kg m/s leftward? Or was there none?
     
  2. jcsd
  3. Sep 7, 2007 #2

    mgb_phys

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    1, correct
    2, No momentum and force are quite different.
    3, Impulse is force * time so has units of Newton seconds ( or kg m/s )
    I don't see how part 3 can be true, the initial carts has ke = 0.5 * 1 * 1^2 = 0.5J
    the second cart has ke = 0.5 * 3* 0.75^2 = 0.84J unless I have made a msitake in arithmetic.
     
  4. Sep 7, 2007 #3

    learningphysics

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    For part 3, impulse given to the small cart is change in momentum of the small cart... so the final momentum of the small cart - initial momentum of the small cart is what you need... careful about directions and signs.
     
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