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Hw help Equilibrium problems

  1. Oct 18, 2005 #1
    Hi, I need some help with these questions:

    A small fish [m=2kg] hangs from one end of a make-shift fishing rod [m=0.5kg] of length 2.5m. The other end of the fishing rod is braced against the ground and held horizontally by a child's hand, 1m from the bottom of the rod. Find the force exerted by the child's hand and the x and y forces on the rod from the ground. (Ans: 65.7N, 65.7N, 24.5N)

    and

    A 160cm tall person lies horizontally on a massless board supported by two scales. 1 is positioned at the person's feet and the other at the person's head. If the scale at head reads 32.8kg and the scale at the feet reads 29.4kg, where is the person's centre of gravity? (Ans: 0.76m from head)

    Thanks
     
  2. jcsd
  3. Oct 18, 2005 #2
    You've got to show a little effort before someone's going to help you, but here's some general advice for any equilibrium problems.
    1) Draw a vector diagram
    2) Resolve all of your vectors into components, and draw a separate vector diagram with these.
    3) Apply Newton's Second Law for each coordinate direction:
    [tex]\sum F_{x}=0 , \sum F_{y}=0[/tex]
    4) Solve the equations you get for the unknowns.
     
  4. Oct 19, 2005 #3
    So far for the first question, I did this:
    Total Torque = 2kg(9.8)(2.5m) + 0.5(9.8)(1.25m)
    I don't know how to find the distance of the Force Hand.
     
  5. Oct 19, 2005 #4
    Centre of gravity

    Assuming
    1. the weight of the person consists of two parts, one at the end of the feet. the other at the end of the head.
    2. the scales are put at the two edges, the feet and the head.
    3. use the formula of centre of gravity.
     
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