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L PreCal

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A car is moving at a rate of 65 miles per housr and the diameter of it's wheels is 2.5ft. Find the number of revolutions per minute the wheels are rotating.

I have no idea where to begin on this question. How do you find rev per min?? Can someone walk me step by step how to answer a problem this?

  • L PreCal -

    First convert miles per hour to feet per second.
    65 mph = 95.3 ft/s

    The rotation rate of the wheels in radians per second, w, is
    w = (speed)/(radius) = (95.3 ft/s)/(1.25 ft)
    = 76.3 radians/s

    Convert that to rpm by multiplying by
    (60 s/min)*[1/(2 pi)] rev/rad)

    729 rpm

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