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Kinematics of Particles

  1. Jul 14, 2016 #1
    1. The problem statement, all variables and given/known data
    Refer to figure please.

    2. Relevant equations
    ∑Fy=0 before string is cut

    3. The attempt at a solution
    I tried summing the two forces in the y direction before the strings were cut which would be the two tensions at a sin40° and minus the weight of the ball(mg). That gave me T in terms of mg. Then I summed the forces when the string was cut and got T minus mgcos40. Then I thought that would be my ratio but my answer didnt match that of the solution. Help Please!!
     

    Attached Files:

  2. jcsd
  3. Jul 14, 2016 #2

    TSny

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    Your approach seems good. Are you sure that you should be using cos40o in the calculation after the string is cut? You left out the details of your calculations and you did not state what you actually got for the tension before and after one of the strings is cut.
     
  4. Jul 14, 2016 #3
    This is what I ended up doing. Does my work look right or did I just happen to get it right? Oh and there should be a mg on the end of my T=0.643 equation. I don't really know why I used mgsinΘ, I just know it gets you the right answer. An explanation on that would be greatly appreciated.
     

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  5. Jul 14, 2016 #4

    TSny

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    In your first diagram your analysis looks good. Here you are taking the y-axis to be vertically upward.

    In your second diagram (one string), what direction are you taking for the y-axis? Also, you should show the gravitational force in this diagram.
     
  6. Jul 14, 2016 #5
    Oh that is what it is. If you take the y axis to be at an angle of 40 degrees then the y component of the weight becomes mg sin40. Makes sense now.
     
  7. Jul 14, 2016 #6

    TSny

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    OK. Good work.
     
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