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Thread: stuck again, can someone help please

  1. #1
    prs
    prs is offline
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    stuck again, can someone help please

    The pedal cranks of a bike are 175mm long and the rear wheel makes 3 turns for each turn of the pedals. If the rear wheel is 700mm in diameter then calculate:

    a) the number of turns made by the cranks while the bike is traveling 1km.

    i did it this way: 700mm/2= R350mm 2x3.14x350mm=2198mm 2198/1000=2.198m

    2.198m x3=6.594m 6.594m/1000m=151.6 the book says 152 rounded up i assume.

    b) the average speed of rotation of the pedals in m/s if the kilometer is covered in 2 min 30 seconds.

    this is the one i need help with please,
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  2. #2
    MHF Contributor
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    I assume the speed of pedals is their speed as they travel along the circle with radius 175mm. So, find the circumference of this radius, multiply it by 152 rotations. This is the total distance traveled by a pedal (in the rotation movement). You also know the time it all took, so you can find the speed.
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  3. #3
    prs
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    i see now, thanks for that emakarov, i get it to 1.11m/s same as the book thanks,
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