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Homework Help: Cow Jumps over the moon!

  1. Oct 9, 2006 #1
    A cow attempts to jump over the moon, but insteads ended up in a orbit around the moon. How can the cow be used to determine mass of moon?
  2. jcsd
  3. Oct 9, 2006 #2
    What physical laws have you learned so far?
  4. Oct 9, 2006 #3


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    You have an awesome teacher to give you questions like this.

    With respect to desA's question, specifically what you know about rotational motion and centripetal force
  5. Oct 9, 2006 #4
    We have studied Newton's Law of Universal Gravitation which I think has to do something with the cow and the moon. Other things that we did a lab on are relationship between centripetal acceleration, radius of orbit and frequency and period of things in circular motion that is uniform.

    ac = v2 / r
    = 4pi2r / T2
    = 4pi2rf2

    Fnet = mv2 / r
    = 4 pi2mr/T2
    = 4pi2mrf2

    FG = Gm1m2 / r2
  6. Oct 9, 2006 #5
    Is the cow in geostationary orbit around the moon (satellite), or is it moving relative to the moon?
  7. Oct 9, 2006 #6
    Although the question doesn't say to me it seems more like a satellite question. I think we have to use something like the speed of the cow around the moon, the radius cow travels and relate to mass of moon.

  8. Oct 9, 2006 #7
    Can someone please help? I still don't know exactly what to do!
    Here's how far I got:
    (G(mass of moon)(mass of cow)) / (distance of cow from centre of moon)2 = (mass of moon)(speed of cow2) / distance of cow from centre of moon)

    Which variables will I need to use?
  9. Oct 9, 2006 #8
    You don't need to numerically solve this, right?
    So just solve symbolically for mass of moon, and whatever's on the other side will be CowInformation that gives you the mass of the moon!

    And I agree that your teacher is too cool for assigning this problem. Who wants points of matter if you have cows jumping over moons?
  10. Oct 9, 2006 #9
    Thank you very much!
  11. Oct 9, 2006 #10
    I agree with 'mbrmbrg'. If you desperately want a numeric answer, then you will need to make assumptions about the missing information, orbit etc. State these assumptions in your answer.
  12. Oct 10, 2006 #11
    I just went with an essay explaining how we would solve for mass. But thanks for all the help. I guess I just needed to know tat its a satellite problem.
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