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*17. Ssm 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 16.7 rev/s? (b) What is the
next shortest time? |
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The blade appears stationary
if the when the light flashes next another blade is occupying the spot the
earlier blade was occupying. So the shortest time occurs when the blades move 120° or 1/3 of a revolution. |
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Next shortest time is 2/3 of a
revolution which would be 2 Dt |
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