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ok here is my question....

a stroboscope is a light that flashes on and off at constant rate. it can be used to illuminate rotating object. if the flashing rate is adjusted right the object ccan appear stationary.

1. waht is shortest time between flashes of light that will makes a 3 bladed propeller appear stationary when it is rotating with angular speed. of 13.8 rev/ s

2. what is next shortest time....?

please explain i read the chapter over and over and over again and i cant find anything to relate tot his problem... maybe im completely missing something but i am extremely lost. please explain in detail as i am desperate to grasp physics...(it is so hard to me) please helpme and explain i really need to understand where answers come from and how to set up problems thank you

2007-03-03 12:40:36 · 3 answers · asked by Anonymous in Science & Mathematics Physics

3 answers

let's say that the blades are identical and equidistant to each other so their separation is 1/3 revolution. further let's assume that the blades are rotating clockwise (counterclockwise will also do) and that our starting point is at blade 1. then, the shortest possible time that the flashes will on and appear stationary is when blade 1 moves on to blade 2 position. in this manner, we will never know if the blades did really move because they're identical. this is the minimum distance that gives the minimum time interval of flashes and still the blades appear stationary. with a formula relating distance, time and speed this shouldn't be a problem anymore....

the next shorter time will be the next shorter distance. this is when blade 1 moves on to blade 3 position in a clockwise direction. meaning it passes blade 2 first then on to blade 3. or that is 2/3 rev. again with distance, time, velocity formula you can now work on this... gud luck...

2007-03-03 16:23:45 · answer #1 · answered by riddler 1 · 0 0

Think of it this way: to appear stationary, the propeller blades have to be in the same apparent positions each time the strobe flashes, right? A 3-bladed propeller is set so that the blades are equidistant; therefore 1/3 revolution apart. So what's the least amount of revolution the propeller can turn to have the blades in the same apparent position? Then, how much would the propeller have to turn to have the blades rotate from position 1 to position 3 (relatively)? Once you have the fraction of a revolution between flashes, use the # of revolutions/sec to work out what fraction of a second the strobe has to flash at.

2007-03-03 12:49:55 · answer #2 · answered by John R 7 · 0 0

You wouldn't be if you had read your text.

2007-03-03 12:51:19 · answer #3 · answered by rico3151 6 · 0 0

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