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Help in vectors

  1. May 19, 2007 #1
    A wrench 30cm long lies along the positive y-axis and grips a bolt in the origin. A force is applied in the
    direction < 0; 3; -4 > at the end of the wrench. Find the magnitude of the force needed to supply 100J of
    torque to the bolt.

    how can i solve it?

    r=<0,.3,0>
    F=<0,3,4>
    T= r X F =100
    then i solved it by finding the det = 100

    |i j k|
    |0 .3 0| = 100
    |0 3x -4x|

    then x = 83.333 N

    but the answer is wrong Why???
     
  2. jcsd
  3. May 19, 2007 #2

    Curious3141

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    Homework Helper

    This is the wrong forum for the question, but no matter.

    How do you find the magnitude of a vector from the components? What you've found (I didn't check your work, so I'll assume it's right) is a scalar multiplier x that satisfies the problem's constraints. Multiply the (0,3,4) vector by the scalar x to get the force vector (three orthogonal components), then find the magnitude using Pythagoras theorem in the usual way.
     
    Last edited: May 19, 2007
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