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Homework Help: How to find the tension of the cord (Conical Pendulum)?

  1. Dec 3, 2009 #1
    1. The problem statement, all variables and given/known data

    Hey, we have this mechanical bat that is attached to a cord and its flying around in a circle on the ceiling. Here is all the information that I have gathered.

    Mass of the bat: 0.1345 kg
    1.609 seconds per revolution
    length of cord: 0.92 m
    height from ceiling: 0.65 m

    Here is what it looks like if it helps. I need to find the tension of the cord.


    Steps and equations would be very helpful.

    Thank you!

    2. Relevant equations

    I don't know what equation to use or where to start. I think it's...

    Tension*cos(x) = mg

    3. The attempt at a solution

    I don't know where to start; I've drawn a picture if you might help anyone.
  2. jcsd
  3. Dec 3, 2009 #2


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    Homework Helper

    That actually might be the right equation, depending on what x is. But you shouldn't just use it without understanding where it comes from. So: (1) how did you come up with that equation? (2) which angle is x?
  4. Dec 3, 2009 #3
    cos^(-1) (0.65/0.92) = ~ 45 degrees

    It is 45 degrees.

    I think I read it somewhere.

    What would be my next step? Just plugging everything in?

    Tension = (9.8m/s^2)(0.1345 kg)/(cos 45) = 1.86 N?
  5. Dec 3, 2009 #4


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    Homework Helper

    I didn't ask what the value of x is, I asked which angle it is, i.e. identify where on the diagram it is. But the fact that you wrote "cos^(-1) (0.65/0.92)" suggests that you identified it correctly. So that works.

    But for your own sake, I'd suggest continuing to think about this until you understand why that's the right answer. "I think I read it somewhere" doesn't really help you get anything out of the problem. (Sometimes it's the best you can do, but this is not one of those times)
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