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Having trouble with Torque HW Problems

  1. Jul 23, 2005 #1
    The 1st Problem is:
    A uniform plank of length 5.9 m and weight 216 N rests horizontally on two supports, with 1.1 m of the plank hanging over the right support (see the drawing). To what distance x can a person who weighs 447 N walk on the overhanging part of the plank before it just begins to tip?

    2nd is:
    A person exerts a horizontal force of F = 174 N in the test apparatus shown in the drawing. (h = 0.33 m.) Find the horizontal force M that his flexor muscle exerts on his forearm.
    Magnitude __________N

    3rd is(hardest one):
    A solid circular disk has a mass of 1.2 kg and a radius of 0.12 m. Each of three identical thin rods has a mass of 0.13 kg. The rods are attached perpendicularly to the plane of the disk at its outer edge to form a three-legged stool (see the drawing). Find the moment of inertia of the stool with respect to an axis that is perpendicular to the plane of the disk at its center. (Hint: When considering the moment of inertia of each rod, note that all of the mass of each rod is located at the same perpendicular distance from the axis.)____________kg . m2

    *Any help will be Appreciated
  2. jcsd
  3. Jul 23, 2005 #2


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    Where are the drawings?
  4. Jul 23, 2005 #3


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    Homework Helper

    When the person is at max distance and at the verge of tipping the normal reaction at the support on other side is just zero, balances the torque due to weight of the plank and that of the person.

    The hint is given but I guess still you have taken moment of inertia of the rods wrongly

    it will be simply 3 x mR^2
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