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B Free Falling bullet duel

  1. Jul 2, 2017 #1
    If two people are free falling from the sky at the same (high) speed, at the same altitude, but about 20 meters away from each other, and one of them has a gun and tries to shot the other, do they aim directly at the other person so they get a hit (because the bullet would also be falling), or do they have to aim lower to hit the target (because the bullet moves through the barrel faster than we are falling)?

    Sorry, i didn't know where to post this. It's just a silly question that had me thinking.
  2. jcsd
  3. Jul 2, 2017 #2
    I've also heard that when armed helicopters are moving sideways fast and firing, they have to compensate for their momentum, so they would have to aim to the side of the target because the bullets would also have momentum (i'm not positive, it's just something ive heard)
  4. Jul 2, 2017 #3


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    At 20m it doesnt matter, but option 1 is correct.
  5. Jul 2, 2017 #4


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    You think maybe it would matter at all how LONG they had been falling? At the start, clearly there's essentially zero difference from stationary. At terminal velocity there would likely be enough wind resistance to make a very small correction helpful.

    My point is, you need to be careful about giving full information in physics problems.
  6. Jul 2, 2017 #5
    Yeah i thought about that, just didn't end up writing it
  7. Jul 7, 2017 #6


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    Stating the exact conditions may be a pain but it does make it easier to give a proper answer. We have to assume ideal conditions unless told otherwise.
  8. Jul 7, 2017 #7


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    This problem is a bit similar to a problem that was in my high school physics text:

    There is a monkey hanging from a high branch and a hunter some distance away on the ground planning on shooting it (don't ask me why). The hunter knows that the moment the monkey sees the muzzle flash, it will let go of the branch. So where does the hunter aim? The answer is: directly at the monkey. Gravity will effect the fall of the monkey and the path of the bullet equally, causing the bullet to intersect with the monkey.

    Now a few years later I was watching my brother and another guy taking turns trying to shoot a tin can tossed into the air with a shotgun. After a few failed attempts, I asked if I could give it a go. Now both of them were experienced hunters, and I had only ever fired a gun just a handful of times, So they weren't expecting much success on my part.

    I took the gun, and remembering the monkey, followed the tossed can with the sights until the moment I saw it reach the top of its arc and pulled the trigger. I hit the can on my first try. My brother looked at me, grabbed the gun back, and said. "Show off!".

    And they say you'll never use the science they teach you in high school in real life!
  9. Jul 7, 2017 #8
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