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# Bullet shot in space, will it move forever … ?

if i fire a bullet in space it will move forever (assuming it won’t hit any celestial object and doesn’t get caught by any aliens). But will it accelerate forever and reach 0.99c or will it accelerate till it attain a certain constant velocity?

Akshay Ramachandran First, there should be something to accelerate the bullet, like some propellant or else if no forces act on it, it moves with a constant speed. But assuming that it is accelerating, then as it increases its speed, the apparent mass of it increases making it difficult for it to accelerate. This can be said in different languages, like the time in its reference becomes slow etc etc. All this stems from theory of relativity whose basic principle is that speed of light is constant independent of the frame of reference because of Maxwell’s law….As a result it won’t reach the speed of light.
Now the next question would be to what speed would it accelerate? The basic answer lies in the amount of propellant you are having. In space to it would be foolish to assume that force experienced by bullet would be constant? There is gravity everywhere which would try to accelerate/decelerate or divert the bullet. Hence it would never be increasing its speed. It requires a lot of propulsion for that and you can calculate the amount of force required to increase the speed of an object from 0 m/s to 0.99 c m/s by integrating using expression of mass as function of velocity

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