physics
posted by Anonymous .
The speed of a moving bullet can be determined by allowing the bullet to pass through
two rotating paper disks mounted a distance d apart on the same axle (Fig. below). From the angular
displacement of the two bullet holes in the disks and the rotational speed of the disks, we can
determine the speed v of the bullet. Find the bullet speed for the following data:
d = 80 cm, = 900 rev/min, and angular displacement = 31.0

φ=31⁰π/180⁰ = 0.54 rad.
n = 900 rev/min =900/60 =15 rev/s
t=φ/ω= φ/2πn=0.54/2π•15=0.006 s
v=d/t =0.8/0.006 = 133 m/s