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Homework Help: A Lunch Tray

  1. Oct 26, 2009 #1
    1. The problem statement, all variables and given/known data

    The mass of the tray itself is 0.187 kg, and its center of gravity is located at its geometrical center. On the tray is a 1.31 kg plate of food and a 0.300 kg cup of coffee. Assume L1 = 0.0610 m, L2 = 0.130 m, L3 = 0.224 m, L4 = 0.365 m and L5 = 0.387 m. Obtain the magnitude of the force T exerted by the thumb. This force acts perpendicular to the tray, which is being held parallel to the ground.


    2. Relevant equations

    3. The attempt at a solution

    Not sure how to start this one. Any suggestions?
    Last edited by a moderator: Apr 24, 2017
  2. jcsd
  3. Oct 26, 2009 #2
    I have no idea what all those lengths are. You probably need the fact that the torque around
    the point where the tray is supported is 0 if it is in equilibrium.
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