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Help my noodle- Falling weight and driveshaft problem

  1. Jan 29, 2007 #1
    Hi folks,

    Am clueless in the area of physical / mechanical engineering, but I need to get an idea of how to calculate the following problem, can someone please guide me to the necessary formulas needed to calculate the following problem

    Assume there is a weighted cylinder suspended by a drive cable which is wound around a drive shaft. Known factors are the weight of the cylinder, weight and diameter of driveshaft, total weight of drive cable, total length of cable wrapped around the driveshaft and starting distance between the driveshaft and cylinder. Ignoring aerodynamic / friction / Heat Issues, just broadly calculated and starting from a static point, once the cylinder is released to fall thus turning the shaft

    How do I calculate

    1) How much energy would the drive shaft produce at a given distance of travel by the cylinder ?

    2) What would the rotational speed of the driveshaft be at a given distance
    of travel by the cylinder ?

    3) Am I correct in assuming (though I know what assumption does) that there is an optimal fall distance whereby the cylinder has reached its maximum potential to deliver power to the driveshaft.

  2. jcsd
  3. Jan 29, 2007 #2


    User Avatar

    Staff: Mentor

    Well, work equals force times distance, power equals force times distance times time, torque is force times length of the lever arm, acceleration is force divided by mass, and circumference is pi times diameter.

    Resistance to roational acceleration is called moment of inertia, though how big of a deal that is depends a lot on the load of whatever this driveshaft is connected to. Can you provide more info about the application?
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