The speed of a moving bullet can be determined by allowing the bullet to pass th

Question

The speed of a moving bullet can be determined by allowing the bullet to pass through two rotating paper disks mounted a distance 89cm apart on the same axle. From the angular displacement 22.6 degrees of the two bullet holes in the disks and the rotational speed 1082 rev/min of the disks, we can determine the speed of the bulet. What is the speed of the bullet? answer in unites of m/s

Explanation / Answer

Find the time using rotational kinematics that pass during which the two holes are made in the paper discs, this will be the time it takes the bullet to move a distance of 0.61m (61cm). It is convenient to convert all data to SI, so the 34.2 angle is: = 34.2(/180) = 0.597rad Then, the angular speeds of the discs are: = 1344rev/min(2rad/1.000rev)(1.000min/60.00s) = 140.7rad/s Then the time taken for the discs to rotate is: = t + 0.5t2-----------------> = 0 t = / = 0.597rad / 140.7rad/s = 0.00424s Since velocity is distance over time: v = d / t = 0.61m / 0.00424s = 140m/s (properly rounded) Slow as bullets go!

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