Three questions about gravity and velocity answered.
If the rifle is fired straight up will the bullet pierce the head of the one who fired it when it comes back down ?
The answer is derived from physics, and is all about gravity’s effect on objects. There is a certain principle in science called a constant. This is a factor that has been determined to remain unchanged with certain caveats. Since conditions on the Earth vary, most constants are said to apply only within a vacuum. Meaning that, with the absence of air resistance gravity will act the same on any body. Therefore, the answer to the above question is obvious. If you stood next to someone and fired directly at them, obviously, the bullet would penetrate. The same is true if a projectile is shot straight up into the air. Acceleration has been measured at a constant 32 ft/sec2. The constant is the same whether the bullet is going up or down. Therefore, when the bullet is ascending it would slow at the same rate at which it speeds up on its descent. If you measured the speed of the bullet at any height along its trajectory both ascending and descending, that speed would be identical. So, the bullet would penetrate because it would have attained the same speed when it reaches the person as it had when it left the rifle.
If a rifle is held exactly perpendicular (i.e., horizontally from the ground) and fired while at the same time a bullet is dropped from the same height, which bullet will strike the ground first?
The question is somewhat convoluted. I am saying that if a person fires a rifle from a height of 6 feet, and a bullet is dropped at exactly that same time from an identical six feet, which of the two bullets (fired from a gun or dropped from the hand) will reach the ground first? Given the properties of gravity discussed in the first question the answer is obvious. They would both hit the ground at the same time. Gravity would pull both bullets toward the Earth at a constant rate (32 ft/sec2.) Since both were enacted upon from the same six foot height, both would reach the ground at the same time.
A plane is flying at a rate of 500 mph. A rifle is mounted outside of the plane and has a muzzle velocity of 500 mph. When the rifle is fired does the bullet leave the gun seeing that they are both (the bullet and the plane) flying at the same rate?
First, ask yourself this. If you are in the same plane, that is traveling 500 mph, and you jump straight into the air, do you go flying backward at 500 mph? You would answer, “Of course not! What a ridiculous question!” However, we hesitate when asked something similar. The speed of anything within or mounted to an object traveling at a certain speed is relative to the speed of the object. If you are within a plane traveling at 500 mph then you are also traveling at 500 mph. If a rifle is mounted on a plane going 500 mph then it is also traveling at 500 mph. The bullet would leave the gun at precisely the same muzzle velocity, that it would, if the gun were sitting on the ground.