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Dynamics in two dimentions

  1. Mar 26, 2015 #1
    1. The problem statement, all variables and given/known data
    Suppose the moon were held in its orbit not by gravity but by a massless cable attached to the center of the earth. Find the tension in the cable.

    2. Relevant equations

    (since the pictures aren't working, I'm just going to post the url to the image) (http://imgur.com/Ktj98f6 [Broken]) All the numbers I used are from the back of the book, shown here. (I used the period, mass and mean radius shown in the image)

    3. The attempt at a solution
    From all the equations, I figured that the new formula using substitution would be F=m((2πr/T)^2)/r) (http://imgur.com/e7QMdTG [Broken])

    Now the answer at the back of the book says 2.01x10^20, but I keep getting 9.08x10^20. I've rechecked my math hundreds of times, and I've also tried plugging in the numbers into the original equations one at a time and I keep getting the same answer. So I figured the only thing that is wrong then is the numbers, but the numbers came straight from the book, so they can't be wrong!
    Last edited by a moderator: May 7, 2017
  2. jcsd
  3. Mar 26, 2015 #2


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    Staff: Mentor

    Why don't you present your math here, step by step? If you also include the constants that you use (there aren't that many!) you can avoid the image links.
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