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Homework Help: Newtons third law problem

  1. Oct 2, 2009 #1
    1. The problem statement, all variables and given/known data

    Two boxes are in contact with each other, both different mases, and are both being pulled by an external force, F.


    I can calculate the acceleration of the system but the Question asks to calculate the force between the mases, ie newtons third law. If you can either draw me the FBD or solve the question that would be helpful. M1 = 1.2 X 10^-3 kg, m2 = 0.147kg, F = 0.6 N

    2. Relevant equations

    F = ma

    3. The attempt at a solution

    a system = net force/total mases in system

    = 0.6 N (1.2 X 10^-3 Kg + 0.147 kg)

    = 4.048 m/s^2

    Fc <----m1---->F

    Fg (Where Fc is the force between the two objects)


  2. jcsd
  3. Oct 2, 2009 #2


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    Homework Helper

    The F appears to act on m2, so on m1 you will only have Fc to the right.
    On m2, you will have Fc to the left, F to the right. This gives you two F=ma equations which you can solve to find the two unknowns Fc and a.

    Or, since you already have the acceleration, you could just calculate the force needed to make m1 accelerate that much. That is just using the known acceleration in the m1 equation.
  4. Oct 2, 2009 #3
    Thanks for your help
  5. Oct 2, 2009 #4


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    Homework Helper

    Most welcome!
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