# physics

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The speed of a moving bullet can be determined by allowing the bullet to pass through
two rotating paper disks mounted a distance
100 cm apart on the same axle. From the
angular displacement 22.9

of the two bullet holes in the disks and the rotational speed
707 rev/min of the disks, we can determine
the speed of the bullet.

• physics -

Assuming a finite speed of the bullet, yet fast enough that the disc cannot make a full revolution while the bullet flies the 100cm, then things are ok.

707rev/min = 707*360°/min = 707*360°/60s = 4242°/s

Since it only rotated 22.9°, we can assume the bullet took 22.9/4242 = 0.00539s to travel 100cm

Speed = 100cm/.00539s = 18552cm/s, or 185.52m/s

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