A drawing shows a device that can be used to measure the speed of a bullet. The device consists of two rotating disks, separated by a distance of d = 0.790 m, and rotating with an angular speed of 65.0 rad/s. The bullet first passes through the left disk and then through the right disk. It is found that the angular displacement between the two bullet holes is θ = 0.360 rad. From these data, determine the speed of the bullet.

Answer 1

The angular separation of the holes, divided by the angular velocity, is the time it takes the bullet to travel between the plates.

T = 0.360/65 = 5.54*10^-3 s

Divide the plate separation but that time for the bullet velocity. It turns out to be pretty slow, less than the speed of sound. Most bullets are much faster than that.
A similar concept has been used to measure the speed of light.

Answer 2

thanks!