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Homework Help: Stupid Question

  1. Oct 11, 2005 #1
    My friends a pre-med student and hes taking basic phyiscs 1. He asked me to do two problems. Can you double check to make sure I did not tell him the wrong thing! :blushing:

    Problem 1.)

    There are two square masses, side by side on a frictionless pond. Mass A is 150kg, and mass b, is 50kg. A force of 100N is applied at mass A, find the reaction force that mass B exerts on mass A.

    So I said on block A: simga(F): (150)a = 100N - F

    and on block B: sigma(F): F = 50a

    since both blocks are in contact, they have to have the same acceleration, so both a's are equal.

    so that means a = F/50, and I plug that into block A's equation.

    150(F/50) = 100 -F

    and so F = 25 N

    Does that sound right?

    I did not have a solution to check for a mistake. And i feel stupid asking this question, but his test is comming up and I dont want him to fail because of what I told him. I was real stupid the first time I did it because I approached it as a statics problem without thinking, I just said oh, its 100N.........errrrrr whoops......... that was dumb of me.
    Last edited: Dec 26, 2005
  2. jcsd
  3. Oct 11, 2005 #2
    Well to me the free-body diagrams look right for sure and the reasoning looks good as well. Your net forces a fine and i they would have the same acceleration. I know it's probably not reassuring to have me say it looks fine, but I'm saying it anyway : )
  4. Oct 11, 2005 #3
    Does anyone else agree, no offense big man? Just makin sure.
  5. Oct 11, 2005 #4


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    Gold Member

    Surely, there's a trick to this question.

    Unless it is a given that the pond is frozen, the masses will not sit on the surface.
  6. Oct 11, 2005 #5
    HAAHAHAHAHAH, i forgot to type frozen......sorry.
  7. Oct 11, 2005 #6


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    Gold Member

    Ah. Then never mind. Carry on.
  8. Oct 11, 2005 #7
    Does it look correct though?

    Theres another problem in his book that is worded funny, and I keep getting a different anwser than what they have. Ill post that problem up too, maybe you can find something im not seeing.
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