Bullet speed?

Question

A jet is flying at the speed of sound: A gun is fired from the rear of the plane: The bullet is traveling at the speed of sound: Will the bullet simply drop to earth?: If not, why not?

Answer 1

Three assumptions must be made about your scenio. First, I assume the gun is fired exactly in the opposite direction of the jet. I assume this, because it sounds like you want to know what happens to the bullet if its muzzle velocity seemingly cancels the velocity of the jet, giving the bullet a velocity relative to the ground of zero miles per hour, both vertically & horizontally. Second I assume that the gun firing the bullet is not in the exhaust flow of the rearward directed airflow of the aircraft engine. Third, which comes from the first assumption, the bullet is not directed into the exhaust flow.

Now, immediately after the bullet leaves the gun barrel, the bullet would have a velocity of zero miles per hour relative to the ground, both vertically & horizontally. All the high pressure gas from the cartridge has dissipated, leaving no further pressure to push the bullet rearward. But the bullet is not zero miles an hour relative to the jet's boundary layer(layer of air actually attached to the metal surface of the jet), the jet's trailing edge shockwave that is attached to the aircraft & the jet's wake(jet wash). The bullet must now penetrate the boundary layer, & the trailing edge shockwave surrounding the aircraft, both which move at the speed of sound relative to the bullet. Finally, the bullet will be influenced to move by the wake left by the jet. The jet's boundary layer & shockwave will try to draw the bullet along with the aircraft for as much as about 1 thousandth of a second, depending on factors such as the pressure strength & thickness of the boundary layer of air attached to the jet, & the strength of the shockwave also attached to the jet. But alas, as powerful as boundary layer aerodynamics & shockwaves are, there is no way the jet's boundary layer & shockwave can accelerate the bullet to follow the jet. The bullet must penetrate the boundary layer & shockwave of the aircraft & finally lose contact with these two influences. Though the jet wake, moving in the jet's direction would be less powerful than boundary layer & shockwave effects, the wake would be able to act on the bullet for a much longer time period. The jet's boundary layer, shockwave, & jet wash do accelerate the bullet horizontally relative to the ground in the direction of the departing jet in the order of 50 to 150 feet per second(about 33 to 100 MPH.), maybe more(?) depending on the mass & coefficient of drag of the bullet. Of course, gravity would also work on the bullet to accelerate it towards the ground & give the bullet a verticle velocity component. Whatever the comparative strengths of the different factors, the bullet would have a nearly parabolic arc relative to the ground till it struck the ground. Departure from a true parabolic arc would depend on bullet mass & coefficient of drag & strength of the jet wash.

Answer 2

Let us talk about reference frames first. The gun and the bullet are in a moving reference frame (the plane) which is traveling in the forward direction at the speed of sound. The bullet is fired in the backward direction also at the speed of sound and hence by the galilean relativity, to an observer on the jet, the bullet would appear to travel in a straight line in the backward direction. But to an observer on the ground who is stationary, the bullet would appear to drop straight down. This is because the backward speed of te bullet would be canceled by the forward speed of the jet.

Answer 3

There can be a difference. However there are a lot of variables. For instance powders burn at different rates and barrels are of different lengths. If a powder is a slow burning one and the barrel is short, the bullet will most likely leave the barrel before all the powder is burned. This tends to create significant muzzle blast and muzzle flash. It is inefficient in terms of generating muzzle velocity. On the other hand if powder burns quickly and the bullet is still in the barrel after the powder is all burned, then the friction of the barrel will slow down the bullet before it leaves the barrel. Load/gun combinations that have significant muzzle blast are not all that fun to shoot and the powerful gasses can disrupt the stability of the bullet as it leave the barrel and thereby diminishing accuracy. Good luck

Answer 4

Ignoring any effects of drag due to air resistance, yes, the bullet will fall straight "down". The frame of reference in this question is the earth. The jet and the bullet are moving in equal and opposite directions with respect to this frame of reference.

Answer 5

if you measured the speed of bullet according to the gun then the speed of the bullet according to an observer on the ground is zero then it simply drop to earth.

Answer 6

Good question! It would depend on if the gun was fired inside the plane or outside. It would lose it's inertia outside of the plane and then fall to the ground but it would have to fly its course if you know what I mean.