Could a projectile shooting downward at near c lift 300lbs?

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Discussion Overview

The discussion revolves around a hypothetical scenario where a 1-pound projectile is shot downward at near the speed of light from a stationary object, with the aim of determining whether it could lift a 300-pound object and how far it might travel as a result. The conversation touches on concepts of momentum, escape velocity, and the implications of relativistic effects.

Discussion Character

  • Exploratory
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant suggests that the momentum of a projectile moving "near c" is exceedingly large, implying it could lift a heavier object.
  • Another participant humorously exaggerates the potential outcome, claiming it could land the 300-pound object on a neutron star and potentially turn it into a black hole.
  • It is noted that the initial speed of the 300-pound object would be significantly greater than 1/300th the speed of the 1-pound projectile, challenging the assumptions made by others.
  • Participants discuss the escape velocity of Earth and suggest that the 300-pound object would travel far beyond the atmosphere if shot at sufficient speed.
  • There is a question about the speed of the object, with one participant correcting another regarding the calculations of speed relative to the speed of light.
  • One participant emphasizes the need to consider relativity, indicating that the initial speed of the 300-pound object would be much greater than previously calculated.
  • Another participant states that the object would leave Earth's gravitational field with a significant velocity, assuming it is small, and would continue moving at a constant speed once free from gravitational influences.

Areas of Agreement / Disagreement

Participants express differing views on the implications of relativistic effects, the calculations of speed, and the potential outcomes of the scenario. There is no consensus on the exact mechanics or results of the proposed situation.

Contextual Notes

Limitations include assumptions about the size of the projectile, the effects of atmospheric drag, and the influence of relativity on the initial speeds of the objects involved.

falafel1995
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If a 1 pound projectile was shot out of a stationary, non-fixed object (downward) near the speed of light (on earth) would it lift the object if it were 300 pounds? If so, how far?
My friend and I were arguing a hypothetical similar to this.
 
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Very far because the momentum of a projectile "near c" is exceedingly large.
 
How far would you like it lifted, sailor?

As you've stated it, and as Curl says, I could land the 300lb object on your favorite neutron star with enough force left over to turn it into a black hole.
 
Of course. The initial speed of the 300-pound object will be 1/300th the speed of the 1-pound object. There's nothing magical about a large size difference.
 
falafel1995 said:
If so, how far?

All the way! More seriously the escape velocity for Earth is ~11kmps, your 300 pound object would be traveling at a speed far greater than this so would shoot straight out of the atmosphere (friction with the atmosphere would cause serious damage but never mind that for now) and straight out of the solar system
 
How fast would this object go, assuming no friction?
 
Last edited:
falafel1995 said:
How fast would this object go, assuming no friction?
PS: I don't think 1/300 the speed of light is not fast enough to escape the solar system with respect to the milky way's gravity, ~525 km/s vs ~302 km/s.

Erm, 1/300th of the speed of light is 1,000km/s. Did you misquote your figures or the calculation?
 
ryan_m_b said:
Erm, 1/300th of the speed of light is 1,000km/s. Did you misquote your figures or the calculation?

I reworked it. It was calculations.
 
You guys didn't consider Relativity. The initial speed of the 300lb object would be much greater than 1/300th that of the 1lb object.
 
  • #10
How far would it go?

It will leave Earth's gravitational field with a fair amount of velocity - whether or not you're taking relativity into account. Of course that's assuming the object is small, I'm not sure how much drag one could get at very large sizes.

Anyway, once it's left the gravitational field, it will keep moving at an almost constant speed (Newton Law #1) - neglecting influences from other bodies. So, as long as it has a clear path, a very long way away indeed.
 

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