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Help With HW problem.

  1. Dec 2, 2009 #1
    1. The problem statement, all variables and given/known data
    1. Centripetal Force: If a 40.0 gram stone is whirled horizontally on the end of a 0.60 m string at a speed of 2.2 m/s. What is the tension in the string?



    3. I did F = 40/0.60 X 2.2. Is that right?
     
  2. jcsd
  3. Dec 2, 2009 #2

    berkeman

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    Staff: Mentor

    Not quite right, but on the right track. Write out the equation you are using symbollically first. Be careful not to drop squared terms. Also be sure to keep your units consistant. Do not mix meters with grams, for example. Keep/convert everything into mks (meters-kilograms-seconds) units.

    EDIT -- Welcome to the PF, BTW!
     
  4. Dec 2, 2009 #3
    Teacher gave us a bunch of equations, so I'm not sure which is the right equation.

    Also, thanks for the Welcome. :smile:
     
  5. Dec 2, 2009 #4

    berkeman

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    There are two main equations that you will use for centripital force (the subject you are studying now). The wikipedia page may clear it up for you a bit. You are given things like linear velocity, mass and radius in your problem statement, I believe...

    http://en.wikipedia.org/wiki/Centripital_force

    .
     
  6. Dec 2, 2009 #5
    This is one:

    75f3b2a3b8aabe3f09d3637dd0cd5f19.png

    Not sure how I should do it though.
     
  7. Dec 2, 2009 #6

    berkeman

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    Not sure what that is. How about trying the first "forumla" on the wikipedia page that I linked for you? Be sure to use all mks units...
     
  8. Dec 2, 2009 #7
    Yeah, the first formula should solve the problem. I got 322.66.
     
  9. Dec 2, 2009 #8

    berkeman

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    Be sure to include units in your equations and results. It helps to prevent math errors and misconceptions.

    Also, if you post your equations and work, we can usually check them here. If you already submitted the answer and it was correct, you don't have to do that for this question.
     
  10. Dec 2, 2009 #9
    It's a work sheet. I did 40 X (2.2)^2/.60
     
  11. Dec 3, 2009 #10

    berkeman

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    Please post the full equation with units. It's honestly meaningless without units. You will learn this in your coming years, grasshopper...
     
  12. Dec 3, 2009 #11
    Haha sorry.

    40 grams X (2.2 m/s)^2/0.60 m = 322.66
     
  13. Dec 3, 2009 #12

    berkeman

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    Staff: Mentor

    grams? Ack.
     
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