A 20 g bullet is fired from a rifle.?

Question

The bullet leaves the 5500 g rifle with a velocity of 150 m/s. How much does the rifle move when it is fired?

Answer 1

Instead of saving 'How much does the rifle move when it is fired?' you are probably asking what the recoil velocity of the rifle is the instant after the bullet is fired.

To find this we employ the law of conservation of momentum.
The initial momentum of the system must equal the final momentum of the system.

Momentum (p) equals the mass (m) of the object multiplied by is velocity (v).
p = m * v

Initially, both the rifle and the bullet are at rest so their initial combined momentum is zero.
p_i = 0

After the bullet is fired, the bullet now posses some amount of 'forward' momentum. To compensate, the rifle must gain momentum in the 'backward' direction.

The momentum of the bullet is:
p_bullet = (20 g) * (150 m/s) = (3000 g m/s) = (3 kg m/s)

We know that the rifle must have a momentum of equal magnitude but in the opposite direction.
p_rifle = (5500 g) * v = -(3000 g m/s)
Solving for v we get,
v = -(3000 g m/s) / (5500 g)
v = -.545 m/s

So the rifle will recoil with a velocity of .545 m/s in the opposite direction of the bullet's velocity.

Answer 2

We lack enough infomration to answer the question. Without knowing the weight of the rifle, and how it is situated there is no way to figure this out.

For every action there is an opposite and equal reaction. The force applied on the bullet is the exact same amount of force that is appled to the rifle in the opposite direction. Yet a 20 grain bullet is very light, tiny in fact. A standard .22 rifle will normlly be 40 grains.

Perhaps you are referring to an air rifle?

Either way, the recoil will be pretty minimal. 150m/s is around 1000 FPS and not paticularly fast and this would be true for even a much heavier bullet. Again I'll go with the .22LR as an example. Out of a 20" barrel I would expect a standard velocity 40 grain bullet to moving about 1,200 FPS

Good luck.

Answer 3

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Answer 4

The rifle does move. It's referred to as recoil, or "kick". I'm not sure of the exact equation, but it's explained in Newton's Third Law of Motion.

This might help:- http://en.wikipedia.org/wiki/Newton's_laws_of_motion

Answer 5

The rifle doesn't move.But now if your talking about the bullet.......................