HELP!!! I cant figure out how to do this one? A stroboscope is a light that flas

Question

HELP!!! I cant figure out how to do this one? A stroboscope is a light that flashes on and off at a constantrate. It can be used to illuminate a rotating object, and if theflashing rate is adjusted properly, the object can be made toappear stationary. (a) What is the shortest time between flashesof light that will make a three-bladed propeller appear stationarywhen it is rotating with an angular speed of 12.6 rev/s?
1 s

(b) What is the next shortest time?
2 s HELP!!! I cant figure out how to do this one? A stroboscope is a light that flashes on and off at a constantrate. It can be used to illuminate a rotating object, and if theflashing rate is adjusted properly, the object can be made toappear stationary. (a) What is the shortest time between flashesof light that will make a three-bladed propeller appear stationarywhen it is rotating with an angular speed of 12.6 rev/s?
1 s

(b) What is the next shortest time?
2 s (a) What is the shortest time between flashesof light that will make a three-bladed propeller appear stationarywhen it is rotating with an angular speed of 12.6 rev/s?
1 s

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

Explanation / Answer

Part A) the frequency is 17.8rev/s, so the period is T=1/f=1/17.8=.0562seconds. but since there are 3 blades on the propeller, itwill have the same orientation every 1/3 of a revolution. sothe minimum time is .0562*1/3=.0187seconds Part B) The propeller will also have the same orientation every 2/3 of arevolution, so the next shortest time is .0562*2/3=.0375seconds

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