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Monkey and the Hunter Paradox

  1. Mar 22, 2006 #1
    The classical monkey and the hunter paradox goes something like this :

    A monkey sitting on a tree top is aimed at by a hunter. As soon as hunter shoots the monkey jumps down. The bullet hits the monkey even when it has jumped because they both fall with same acceleration viz. g.

    My question is:

    If the monkey does not jump, will the bullet still hit him?
    Does the hunter have to aim a little higher to get the correct shot?
  2. jcsd
  3. Mar 22, 2006 #2
    If a hunter aims at a stationary target in a zero-gravity enviorment, he will hit the target.

    If a hunter aims at a stationary target on earth, then the bullet will follow a parabolic descending trajectory, like any falling object; (of course it will be very slight - the forward velocity will at any time be orders of magnitude greater than the downward velocity). Thus he will miss the target - the bullet will have fallen slightly and will hit below target.

    Has this answered your questions?
  4. Mar 22, 2006 #3
    The hunter misses the target in gravity, but then how does one get a correct shot?
  5. Mar 22, 2006 #4


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    Given the necessary information you can compute the angle needed. What Information do you thing you need?

    You can always do it by trial and error. This would correspond to the practice called "sighting in" used by people who shoot rifles.
  6. Mar 22, 2006 #5
    The information needed would be the velocity of the bullet as it leaves the rifle, height at which the monkey is present.

    I was unaware of the practice of ''sighting in''. But does that mean an experienced hunter can miss a target, if the location of hunting changes (changing the g value)?
  7. Mar 22, 2006 #6


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    In practice, if the target is not far away, the distance over which the bullet falls (as compared to go in a straight line) is rather small.

    To give you an idea, assuming the velocity of the bullet is ~1000m/s, and the target is 100 m away, this will take the bullet 0.1 s to reach the target. In 0.1s, it will also fall g t^2/2 = 0.05 m = 5cm.



  8. Mar 22, 2006 #7
    5 cm is quite an high value when the precision is concerned...then how does an shooter who doesn't know any physics will make it..if ofcourse he has 1 shot.
  9. Mar 22, 2006 #8


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    And he's hunting mice :smile:
  10. Mar 22, 2006 #9
    I've done some shooting and sighting in. Idealy you want to sight in a rifle such that a flat horizontal shot will rise ever so slightly as it leaves the gun. In this manner you can split the inaccuracies to fall either above or below your target depending on the distance. For instance if you sight a 30-30 to hit dead on at ~100 yards then depending on the target distance less than ~100 yards it can hit ~1 inch above or below the intended target. Generally speaking your inaccuracy is half of the bullet fall within the ideal range it is sighted for. Beyond that range accuracy drops off exponentially. Ideal ranges are determined by things such as mussel velocity, loss of velocity due to resistance, bullet rotation, bullet aerodynamics, and windage. 30-30s don't work exactly as expected by the physics for these reasons but generally all rifles are sighted to split the difference for an ideal maximum range.

    Oh the question.. Sighted this way if the monkey jumped you miss unless the monkey was outside the intended range of the rifle.
    Last edited: Mar 22, 2006
  11. Mar 22, 2006 #10


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    A hunter who plans on shooting at things 100 yds away or more must account for the drop, though whether they understand the physics behind it is another matter.

    I don't have a lot of experiece with rifles, but I used several when I was in the Navy and all had distance compensation on their open sights. It was precalculated, so all you had to do was dial-in the distance and that raised the rear sight the appropriate amount.
  12. Mar 22, 2006 #11


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    It is the mussel velocity that always messes me up. By the time I've run down to the beach with a measuring tape and a calendar, and back again, the monkey is invariably gone.
  13. Mar 22, 2006 #12


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    :rofl: :rofl: :rofl: Too funny.
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