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Homework Help: Adjacent Blocks: What is the mag of the force due m1 on m2?

  1. Oct 6, 2008 #1
    1. The problem statement, all variables and given/known data

    Image1.jpg

    2. Relevant equations

    f=ma

    3. The attempt at a solution

    I got the acceleration by:

    (f1-f2)/(m1+m2)=a

    Now the first two q's I just cannot figure out.

    1.5*4=nope
    1.5/.367347*4=nope
    1.5/.367347+4=nope
    4*.367347=nope
    2.66667-.647059=nope...................ah!
     
  2. jcsd
  3. Oct 6, 2008 #2

    Redbelly98

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    You're right that f=ma is the way to go here, and I agree with a=0.3673 m/s2***

    Now that you know "a", and of course "m" for each mass, what does f=ma tell you about each mass?

    ***Uh, that should be written 0.37 m/s2 when given as an answer. But keep those extra digits for doing calculations involving "a"
     
  4. Oct 6, 2008 #3
    f=ma
    (m1)1.5
    (m2)3.4
    (a).367347
    (m1+m2)=4.9
    (m1-m2)=1.8

    1.5*.367347=nope
    4.9*.367347=nope
    1.8+.367347=nope

    lost.. what am i doing wrong?
     
  5. Oct 6, 2008 #4
  6. Oct 6, 2008 #5

    Redbelly98

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    You seem to be plugging in numbers at random, and not thinking about what they mean.

    In general, when you multiply a mass times its acceleration, that gives you ______ ? (No numbers here, use words.)
     
  7. Oct 6, 2008 #6
    it of course gives you force, the numbers represent my understanding of the words, I tried different combonations of adding subtracting and dividing mass, force and acceleration for the whole system but smartwork is telling me they are the wrong answers.
     
  8. Oct 6, 2008 #7
    i do appreciate your help btw thank you.
     
  9. Oct 6, 2008 #8

    Redbelly98

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    You're welcome.

    Yes, it gives you the force. And if there are 2 or more forces acting on the object, it gives you the net force.

    Can you use the fact that you are really calculating net force on a mass, and get from there to what is being asked for?
     
  10. Oct 6, 2008 #9
    O.k. got it thanks!

    the sum of the x forces is:

    F-m1*a=3.4N

    or

    4N-(1.5kg*.367347m/s^2)=3.4N

    and it is the same when you try the second mass:

    F+m2*a=3.4N

    or

    2.2N+(3.4kg*.367347m/s^2)=3.4N

    Thanks for your help.
     
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