What Happens When a Projectile Is Fired Opposite to a Moving Car?

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Discussion Overview

The discussion revolves around the scenario of firing a projectile from a moving vehicle, specifically a truck, and the resulting motion of the projectile relative to both the truck and an observer on the ground. The scope includes conceptual reasoning about projectile motion and relative velocities, with some participants introducing variations and hypothetical situations.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant poses a scenario where a projectile is fired from a truck moving at the same speed, questioning the resulting motion.
  • Another participant suggests that if the projectile is fired in the opposite direction, it would appear to fall straight down to an observer in the truck.
  • Some participants argue that air resistance would affect the projectile's motion, causing it to fall behind before hitting the ground.
  • A participant introduces a variation involving a train moving at speed X, suggesting that to an observer on the ground, the projectile would seem to fall straight down.
  • There is a discussion about the speed of different projectiles, including paintball guns and their velocities compared to vehicles.
  • One participant mentions the potential of high-speed trains outpacing certain projectiles, indicating that "projectile" does not necessarily imply high velocity.
  • Another participant shares anecdotal experiences with paintball guns and modifications, emphasizing the variability in projectile performance.

Areas of Agreement / Disagreement

Participants express various views on the motion of the projectile, with some agreeing on the basic principles of relative motion while others introduce different scenarios and variables, leading to multiple competing perspectives. The discussion remains unresolved regarding the exact outcomes and effects of air resistance.

Contextual Notes

Participants mention ideal conditions and the influence of air resistance, indicating that practical outcomes may differ from theoretical predictions. There are also references to different types of projectiles and their speeds, which may affect the discussion's context.

Masterior
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[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.. that's what happens when i get bored)

thanks
 
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All I see is messed up html text that might try to run a swf file. Was the site hacked?
 
it seems that password is needed.
 
hm.. try it again i changed some things
 
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.
 
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
 
ok, thanks for the help.. sorry for the "fishy-ness" of the link
 
Where is the firer? On the truck? or on the ground?

then to an observer in the truck the bullet would appear not to move horizontally but "fall straight to the ground".
Well, maybe ideally. In practice, air resistance would cause the bullet to fall behind before it hit the ground.
 
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?
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.
 
  • #10
SF said:
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.
Well, that'd be a train moving at several thousand feet per second.
Pretty hard to put into practice...
 
  • #11
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.
 
  • #12
Paintball guns aren't that fast. I think you can use a normal road car for that one.
 
  • #13
Well, when I was working at the paintball club, repairing and rebuilding the markers, we chronoed them at 360fps. They're capable of more.
 
  • #14
For the sake of the experiment, we'll use old USSR-made paintball guns, not state of the art paint bazookas :)
 
  • #15
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.
 

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