# Acceleration in vacuum

If a bullet is fired from a gun in vacuum(assume no gravity, no resistance).

why is it that the bullet accelerates 0 to v inside the barrel but as it exit the muzzle it stop accelerating.

Isn't when the bullet exit , it exit with some force which give it a initial velocity v.

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As combustion gases inside the barrel expand they exert a force on the bullet, as long as the force is applied the bullet accelerates. When the bullet exits the muzzle the combustion gases can escape and will disperse in the vacuum.
Because the gas can no longer exert a force on the bullet it stops accelerating and maintains a constant velocity. It does not keep some of the force that initially accelerated it.

out of the muzzle, there is no force putting on the bullet --> a = 0

It seems a bit difficult as the last force available to the bullet as it exit, will not provide acceleration.

Because many will think that when a stone is thrown it will accelerates to some velocity and then deaccelerate.

But thats right. Thanks for the answer.