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Homework Help: Impulse/momentum concept questions

  1. Oct 5, 2007 #1


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    1. The problem statement, all variables and given/known data


    (hopefully all can be read)

    2. Relevant equations

    p = mv

    impulse = m(change in v)

    3. The attempt at a solution

    Top Left: My initial guess is they should all be the same since all cars on the roller coaster feel the same affect of gravity for the same distance and time (assuming there is no engine on the cars themselves). However, I cannot figure out how to use momentum or impulse to solve it.

    Top Right: First of all I dont understand how they both move towards each other if they both pull equally. Shouldnt the forces cancel themselves out and neither moves? As for the 2nd part, I believe only the girl on left moves towards the guy and she will move the entire 6 meters.

    Bottom Left: I believe this is the same question as the roller coaster one but instead of cars, we have links on a chain so my answer would be the same as the first question - both blocks hit at the same time.

    Bottom Right: Hard to read the question but I believe the dots represent the center of masses of each truck. Which will topple over? My answer is C because it has the highest center of mass, however again I cannot figure out how to use impulse or momentum to solve it.

    Any help on these would be appreciated. Trying to understand a new concept is a little tricky sometimes. Thanks.
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Oct 5, 2007 #2


    Staff: Mentor

    For top left I would use conservation of energy rather than impulse/momentum.
  4. Oct 6, 2007 #3
    For the top left answer is already given.

    For the top right you should do it by the center of mass. Since no external force is applied the center of mass remains at the same place.So in the second case also both move three meters.

    Now for the bottom left both the blocks will fall at the same time.It is a free fall.

    For the bottom right, i cannot read the question.
  5. Oct 6, 2007 #4


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    so then my answer should still be correct, right? since PE (top) = KE (bottom) all the cars should have the same speed at the bottom.
  6. Oct 6, 2007 #5


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    how is that possible? how can he move if shes not pulling on the rope?
  7. Oct 6, 2007 #6


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    Science Advisor
    Homework Helper
    Gold Member

    She is pulling on the rope, just with her waist instead of her hands. He pulls 'hand over hand', leaving six meters of rope on the ground behind him when they meet at the 3 meter mark.
  8. Oct 6, 2007 #7
    Also remember that there is no friction.
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