Trajectory Question ```Name: Robert Status: other Age: 50s Location: N/A Country: N/A Date: 1999 ``` Question: If a rifle is aimed perfectly straight in the air and a bullet is shot out of the muzzle at 5000 feet per second. If the trajectory is straight up and the bullet comes straight back down. How fast will the bullet be traveling when it falls back down and reaches the same point that it left the muzzle at? I seem to remember from my college days, it attains the same speed as it had when it left the muzzle. Replies: Ignoring the effects of drag (i.e., wind resistance), the total energy of the bullet (kinetic energy plus gravitational potential energy) remains constant, so it will regain all of its muzzle speed when it returns to earth. Tim Mooney Two problems. The first is that the bullet experiences drag when it moves through the air, so that it loses kinetic energy. As a result, it will not be traveling quite as fast at the end as at the beginning of its trajectory, even if they are at the same height. This problem would be eliminated if there were no atmosphere. In that case, the speeds at the beginning and gthe end would be the same, just the directions would be different. The second problem is that the earth is rotating; a bullet fired straight up will appear to drift toward the west a bit. This would be most signbificant at the equator and least at the poles. Richard Barrans Jr., Ph.D. It will be less than the initial muzzle velocity because of the drag due to air. That drag reduces the velocity as the bullet rises and as it falls. Dr. Bradburn Click here to return to the Physics Archives

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