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Homework Help: Another torque question

  1. Jan 20, 2016 #1
    1. The problem statement, all variables and given/known data
    A meter stick (thus, the length of the stick is exactly 1 meter!) is supported by two supports. Support A is located at the 20-cm mark, and support B is at the 68-cm mark. You can assume that the mass of the meter stick is uniformly distributed along the length of the stick. There is also a block on the meter stick, located at some distance x from the left end of the stick (the left end corresponds to the 0-cm mark).

    For this problem, the block starts off at the x = 0-cm mark. In other words, the block starts at the left end of the meter stick. With the block in that position, the meter stick is just about to tip over. Support A exerts an upward 15 N force on the meter stick, and support B exerts no force on the meter stick.

    Determine the weight (not the mass, the weight) of the block, in newtons.
    Determine the weight (not the mass, the weight) of the meter stick, in newtons.
    What is the value (in cm) of the largest x that the block can have so that the meter stick is just about to tip over? Hint: think about what the two supports forces must be in that situation

    2. Relevant equations
    T=Force times distance from center of mass

    3. The attempt at a solution
    So I know I need to find the pivot point, so as to know the distance. Once I have that, I am really not sure what to do. I am just really lost on this question.
  2. jcsd
  3. Jan 20, 2016 #2


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    Staff Emeritus
    Science Advisor
    Homework Helper

    First, I would draw a simple sketch of this meter stick, showing the supports and the movable block.

    For the first part of the question:
    Hint: By carefully picking the point about which you write your torque equation (not necessarily one of the supports), you won't need to know the weight of the block, initially.

    Write some torque equations and see what drops out.
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