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Homework Help: Question in rotational motion

  1. Jan 2, 2013 #1
    1. The problem statement, all variables and given/known data
    A vacuum cleaner belt is looped over a shaft of radius
    0.45 cm and a wheel of radius 1.80 cm. The arrangement of the
    belt, shaft, and wheel is similar to that of the chain and sprockets in
    Fig. Q9.4. (Just like a bicycle).The motor turns the shaft at 60 rev/s, and the moving
    belt turns the wheel, which in turn is connected by another shaft to
    the roller that beats the dirt out of the rug being vacuumed. Assume
    that the belt doesn’t slip on either the shaft or the wheel. (a) What
    is the speed of a point on the belt? (b) What is the angular velocity
    of the wheel, in rad/s??

    2. Relevant equations

    Rotational motion equation

    3. The attempt at a solution

    I don't know whether v should be the same for both or w (omega) should be the same for both???
  2. jcsd
  3. Jan 2, 2013 #2
    It might be a little easier if you posted some diagrams.
  4. Jan 2, 2013 #3
    I think they have the same linear velocity V because if you think about it the belt which is wrapped around these two wheels, the distance traveled on the belt has to be the same for both in the same time interval (otherwise it would fall apart). However the omega is not the same for both, you can see this from V = WR, they have the same V but will have different omega if the radius is different for both wheels. You can also think about it the smaller wheel has to turn more times to get through more of the belt in the same time interval the larger wheel has to turn only a little to get through the same distance of belt.
  5. Jan 2, 2013 #4


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    The speed of all parts of the belt must be the same or it will stretch.

    You know the rpm (angular velocity) and dimensions of the small shaft so can write an equation for the speed of a point on it's outer edge. That's the same speed as the belt.

    Work same equation backwards to give the angular velocity of the larger pulley.

    Edit: If you avoid the temptation to substitute values early on you might stumble on a short cut as a lot will cancel.
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