How many times does the second propeller spin?

How many times does the second propeller spin?

• A. One time
• B. Two times
• C. 1 1/2 times counterclockwise
• D. Three times

Answer: (C)

When two propellers are linked by a belt drive, the speed of the driven propeller depends on the sizes of the two pulleys. The belt imposes the same belt speed on both pulleys, so the angular speeds relate as ω2 = ω1 × (R1/R2) = ω1 × (D1/D2). Here the driving pulley has a diameter larger than the driven pulley by a ratio of 12 to 8, which is 3/2, so the driven propeller spins 1.5 times for every full turn of the driver. The direction of spin depends on how the belt is arranged: a crossed belt makes the driven rotation opposite to the driver, while an open belt would keep the same direction. Since the second propeller is stated to spin counterclockwise while the first is presumably clockwise, that indicates a crossed belt, but the speed relation (1.5 times) comes from the diameter ratio. So, for one complete turn of the first propeller, the second completes one and a half turns.

When two propellers are linked by a belt drive, the speed of the driven propeller depends on the sizes of the two pulleys. The belt imposes the same belt speed on both pulleys, so the angular speeds relate as ω2 = ω1 × (R1/R2) = ω1 × (D1/D2). Here the driving pulley has a diameter larger than the driven pulley by a ratio of 12 to 8, which is 3/2, so the driven propeller spins 1.5 times for every full turn of the driver.

The direction of spin depends on how the belt is arranged: a crossed belt makes the driven rotation opposite to the driver, while an open belt would keep the same direction. Since the second propeller is stated to spin counterclockwise while the first is presumably clockwise, that indicates a crossed belt, but the speed relation (1.5 times) comes from the diameter ratio.

So, for one complete turn of the first propeller, the second completes one and a half turns.