A stroboscope is a light that flashes on and off at a constant rate. It can be u

Question

A stroboscope is a light that flashes on and off at a constant rate. It can be used to illuminate a rotating object, and if the flashing rate is adjusted properly, the object can be made to appear stationary. (a) What is the shortest time between flashes of light that will make a three-bladed propeller appear stationary when it is rotating with an angular speed of 14.2 rev/s?
1 s

(b) What is the next shortest time?
2 s (a) What is the shortest time between flashes of light that will make a three-bladed propeller appear stationary when it is rotating with an angular speed of 14.2 rev/s?
1 s

(b) What is the next shortest time?
2 s

Explanation / Answer

With a 3 bladed prop, it will also appear still when one blade moves 1/3 of the way around also. So the slowest strobe rate will be 1/3 of 14.2 Hz The next slowest is when the propeller moves through 2/3 of a revolution.

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