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Cars and projectiles

  1. Aug 27, 2006 #1
    [link looks fishy - deleted by moderator]

    ok so one of my friends asked this question..

    if you are riding in the back of a truck, and the truck is traveling at the speed of a projectile, what happens when the projectile is fired the opposite direction that you are traveling?

    (see website.. thats what happens when i get bored)

    thanks
     
    Last edited by a moderator: Aug 28, 2006
  2. jcsd
  3. Aug 27, 2006 #2

    rcgldr

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    All I see is messed up html text that might try to run a swf file. Was the site hacked?
     
  4. Aug 27, 2006 #3
    it seems that password is needed.
     
  5. Aug 27, 2006 #4
    hm.. try it again i changed some things
     
  6. Aug 28, 2006 #5

    russ_watters

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    The link looks like a hack/trojan attempt to me, but the answer to the question is simple: if a projectile is fired at the same speed as a moving truck (according to the truck) but in the opposite direction, it falls straight to the ground.
     
  7. Aug 28, 2006 #6

    HallsofIvy

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    If a projectile is fired, relative to the ground, at the same speed as a truck is going, relative to the ground, and in the same direction as the truck, then to an observer in the truck the bullet would appear not to move horizontally but "fall straight to the ground".

    However, if the projectile is fired in the opposite direction the projectile would appear, to an observer in the truck, to be moving horizontally twice as fast as relative to the ground
     
  8. Aug 28, 2006 #7
    ok, thanks for the help.. sorry for the "fishy-ness" of the link
     
  9. Aug 28, 2006 #8

    DaveC426913

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    Where is the firer? On the truck? or on the ground?

    Well, maybe ideally. In practice, air resistance would cause the bullet to fall behind before it hit the ground.
     
  10. Sep 3, 2006 #9

    SF

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    I've thought about this too, but with a twist.

    If the train moves with speed X, and a projectile is fired countrary to the direction of travel also with speed X, to an observer on the ground the bullet would seem like it falls straight down as if someone just let it drop.

    No friction this time :) Ideal case in practice too.

    It would be really cool of you'd fire a machine gun.
     
  11. Sep 3, 2006 #10

    DaveC426913

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    Well, that'd be a train moving at several thousand feet per second.
    Pretty hard to put into practice...
     
  12. Sep 3, 2006 #11

    Danger

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    Actually, Dave... one of those Japanese 'bullet trains' going one way just might outpace a paintball gun, arrow, or similar. 'Projectile' doesn't necessarily imply a high-velocity firearm.
     
  13. Sep 3, 2006 #12

    SF

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    Paintball guns aren't that fast. I think you can use a normal road car for that one.
     
  14. Sep 3, 2006 #13

    Danger

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    Well, when I was working at the paintball club, repairing and rebuilding the markers, we chronoed them at 360fps. They're capable of more.
     
  15. Sep 3, 2006 #14

    SF

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    For the sake of the experiment, we'll use old USSR-made paintball guns, not state of the art paint bazookas :)
     
  16. Sep 3, 2006 #15

    Danger

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    You should have seen the stuff that one of my buddies is into. They take paintball very seriously. His personal favourite weapon is a 7mm Remington that has been rebarrelled to .68 caliblre. They use black powder blanks behind the paintballs instead of CO2 cartridges. His barrel is also rifled, and they make their own extra-thick paintballs. Using a 10x scope on his rifle, he drilled an enemy in the forehead at 150 yards. And Perish forbid you should ever trip one of his claymores or bouncing-betties.:surprised
     
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