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Newtons third law question

  1. Mar 27, 2013 #1
    1. The problem statement, all variables and given/known data

    two hockey players are standing on ice. Player A is 100kg and player B is 112kg, Player A pushes B with 40N and player B pushes A with 50N.

    what are the action/reaction forces?
    what are the accelerations?


    2. Relevant equations

    F = ma


    3. The attempt at a solution

    player A has a force of 50N on him plus the reaction from his own force of 40N making 90N left

    90N on each player in opposite directions, 90/100 = 0.9 m/s^2 and 90 /112 = 0.8 m/s ^2 in other direcction


    Please help me!!!
     
  2. jcsd
  3. Mar 27, 2013 #2

    mfb

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    Looks fine.
    Where do you need help?
     
  4. Mar 27, 2013 #3
    Is this correct?
     
  5. Mar 27, 2013 #4
    The diagram looks like this:


    http://i.imgur.com/LP6NfNw.jpg


    some people are telling me that it is 10N left on the 100kg object?

    Is it correct that I consider on each object the force of its own reaction + the force applied to it so that on 100kg I have 90N left and on 112kg I have 90N right?
     
  6. Mar 27, 2013 #5

    mfb

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    I would interpret the problem statement in that way, yes.

    Please don't write PMs related to homework threads, they are just annoying.
     
  7. Mar 27, 2013 #6

    Andrew Mason

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    This is a poor question, in my view. What does it mean that A applies 40 N of force to B and B applies 50 N to A? How? They will always apply the same magnitude of force to each other - even if one pushes harder than the other.

    AM
     
  8. Mar 28, 2013 #7

    ehild

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    The players are extended bodies, and push each other at different points. See picture.

    ehild
     

    Attached Files:

  9. Mar 28, 2013 #8

    Andrew Mason

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    Ok. But that does not mean that they push each other with different magnitudes of force.

    An astronaut in space may push off with his legs against one end of the spaceship with 100 N force. But that does not mean that the spaceship applies 0 force to the astronaut. On the contrary, the spaceship applies 100N of force to the astronaut. There is no difference between "apply" and "push" here.

    AM
     
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