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Homework Help: Long jump velocity question

  1. Jul 14, 2006 #1
    I have what probably sounds like a simple question...here it is:

    You desperately want to qualify for the Olympics in the long jump, so you decide to hold the qualifying event on the moon of your choice. You need to jump 7.52 m (and conveniently beat Galina Chistyakova's record) to qualify. The maximum speed at which you can run at any location is 5.90 m/s. What is the magnitude of the maximum rate of freefall acceleration the moon can have for you to achieve your dream?

    Φ = 0.5arcsin [-a_y∆x/v^2]
    there are other equations but I don't know which ones to use
    Last edited: Jul 14, 2006
  2. jcsd
  3. Jul 14, 2006 #2
    Do you know projectile motion analysis ?

    Hint: Use the equation for maximum range .
  4. Jul 14, 2006 #3
    We've been studying projectiles, but nothing too indepth. I tried to use the first equation I listed (the maximum range one...?), but I ran into trouble with the angle measurement.
  5. Jul 14, 2006 #4
    At what angle does the projectile or jumper attain maximum range ?
  6. Jul 14, 2006 #5
    No idea...is that something the question should provide?
  7. Jul 14, 2006 #6
    In your first expression, ∆x becomes max. when sin2Φ = 1.
    Therefore Φ equals ___ ?
  8. Jul 14, 2006 #7
    Φ = 45 degrees
    (because sin2Φ = 2sinΦcosΦ
    and when Φ = 45 ... it's 2*(1/root 2)*(1/root 2)...which is 1)
    if Φ = 45 degrees, then the a_y = -4.63 m/s^2
    therefore, the magnitude is 4.63
  9. Jul 14, 2006 #8
    One thing I'm not quite clear on is how "∆x becomes max. when sin2Φ = 1" ...I'm probably just not thinking clearly about it. The answer is asking for the magnitude, not the direction, so the sign of the answer doesn't matter.
  10. Jul 14, 2006 #9
    Yes, you are right :smile:
    Edit: What are the values that sine function can take ?
  11. Jul 14, 2006 #10
    The sine function can take values of 0 to 1. Ah and it can't be 0, so one is the maximum, but when sinx = 1, cosx = 0. Therefore, it has to be somewhere in between. Now the question is how to indicate such logic concisely when doing a problem. (I very much appreciate your help, by the way!!!)

    Edit: sine can take values of -1 to 1...oops
    Last edited: Jul 14, 2006
  12. Jul 14, 2006 #11
    Just got it. When Φ = 45 degrees, that's creates the maximum value because we're dealing with a double-angle. So that explains why the answer is highest when Φ = 45 degrees.

    Thanks again for your help!!! :biggrin:
  13. Jul 15, 2006 #12
    Correct and you're welcome :smile:
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