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Homework Help: Force Between Carts

  1. Sep 16, 2009 #1
    1. The problem statement, all variables and given/known data
    The problem is to give the forces that two carts experience in 4 different situations. A java applet was provided to simulate the situations which is http://physics.bu.edu/ulab/prelabs/prelab_forces_1.html" [Broken], but I will describe them as well, just in case you don't have java or don't want to load the applet.

    1) Two carts of equal mass colliding. The first of the carts is in motion toward the second, which is stationary. Upon collision, the first cart stops moving and the second begins moving.

    2) Two carts of unequal mass colliding. A cart with a mass of 1 unit is moving toward a stationary cart with a mass of 3 units. Upon collision, they both move in opposite directions with respect to each other.

    3) One cart of mass 1 unit is pushing a cart with mass of 3 units.

    4) One cart is pulling another cart of equal mass using a rope.

    2. Relevant equations
    I suppose F = ma

    3. The attempt at a solution

    1) Since they are of equal mass I am assuming equal force felt by both carts upon collision.

    2) Since the bigger cart has more mass, it should exert more force, therefore the smaller cart should feel more force.

    3) The lighter cart should be feeling more force since the heavier massed cart has a greater force.

    4) The forces should be equally felt since both carts are feeling the tension from the rope attached to an equal-massed cart.

    Thanks for any help you could give me, and I'd like to know the reasoning behind any corrections you have if it's not too much trouble (since I'd like to learn the stuff rather than just get answers).
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Sep 16, 2009 #2


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    Homework Helper

    In all four cases, the first cart exerts the same force on the second as the second does on the first. This is a direct restatement of Newton's third law. I doubt this was supposed to be your answer, however; what did the question say, word-for-for?
  4. Sep 16, 2009 #3
    This is literally the exact page: http://physics.bu.edu/ulab/prelabs/prelab_forces.html

    But I will go ahead and quote the questions:

    Did you check out the simulation link I posted? I'm sure reading about it in text just doesn't have the same effect: http://physics.bu.edu/ulab/prelabs/prelab_forces_1.html
  5. Sep 16, 2009 #4


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    Ah, so the lab is indeed talking about the forces exerted by the carts on each other, not the total force felt by each cart. In that case, forces are equal in all four simulations. It's a property of the universe that whenever two objects interact, they must exert the same force on each other but in opposite directions. That's known as Newton's third law.

    (By the way, I did check out the simulation, but it doesn't change my answer.)
  6. Sep 16, 2009 #5
    Alright, thanks man, I appreciate it!
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