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Homework Help: Acceleration and tension

  1. Sep 29, 2007 #1


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    1. The problem statement, all variables and given/known data
    2 crates shown in the figure below are on a horizontal frictionless surface. The woman is wearing golf shoes for traction as she applies a horizontal force of f= 50.0 N to the 6.00kg crate. The ropes are of negligible mass.

    a) draw a free body diagram for each of the crates and the woman and for each force, indicate what body exerts that force.

    b) What is the acceleration of the 6.00kg crate?

    c) what is the tension T in the rope connecting the 2 crates.

    http://img265.imageshack.us/img265/8195/picture2xo8.th.png [Broken]
    2. Relevant equations

    F= ma

    I don't know the equation for tension though...

    3. The attempt at a solution

    Well would the free body diagram show the forces going in different directions?
    I assume so but for the other box and woman how would that look?

    b.) F= ma
    I know it's that equation but how do I find out how much is the acceleration since there are 2 boxes but I have to find the acceleration of the first one?
    do I add the masses and assume that the acceleration is the same for both? I think that it would be logical ..so

    F= 50N
    m= smaller box + larger box = 4.00kg + 6.00kg= 10.00kg= 10,000g

    F= ma
    50N= 10,000g*a

    a= 5e-3m/s^2

    Is this correct?
    c.) for this part I have no idea how to find tension since it wasn't explained in class.


    P.S I really need to do this question by today...
    Last edited by a moderator: May 3, 2017
  2. jcsd
  3. Sep 29, 2007 #2
    for the woman, it would be 50N on to the left(thats how much she applies) n 50N to right(thats frictional force, remember she doesnt move).
    for the other box, only force acting is tension towards right(thats why it accelerates)

    your solution to B) is correct

    its the same as applied by the woman, ie 50N
  4. Sep 29, 2007 #3
    oh no, look for the units in your calculations, i missed them in first go
  5. Sep 29, 2007 #4


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    So is the units incorrect or the problem??

    so there isn't any calculation for tension?? it's just 50 N??

    and wouldn't the acceleration be in m/s^2...why is it incorrect?
  6. Sep 29, 2007 #5


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    Can someone PLEASE help me with this question?? I need to finish this question by today and I need help...or at least I think I do

    ~Thanks alot~
  7. Sep 30, 2007 #6
    F is kg*m*s^(-2).
    acceleration is m*s^(-2)
    so mass should be in Kg, not in "grams", as you have taken
    and thus acceleration comes out to be (with a lil help from my calculator) as 5m/s^2

    also tension is equal to the force applied, so 50N
  8. Sep 30, 2007 #7


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    Oh okay Thanks for clearing that up for me =D
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