Stupid Question

  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. 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. Does anyone else agree, no offense big man? Just makin sure.
     
  5. DaveC426913

    DaveC426913 16,303
    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. HAAHAHAHAHAH, i forgot to type frozen......sorry.
     
  7. DaveC426913

    DaveC426913 16,303
    Gold Member

    Ah. Then never mind. Carry on.
     
  8. 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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