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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
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Update: June 2012
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