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Homework Help: Triangle tangent to circle problem using derivatives

  1. Oct 12, 2011 #1
    1. The problem statement, all variables and given/known data Tangent.jpg

    A metal bar of length l in the figure below has one end attached at a point P to a circle ofradius a < l. Point Q at the other end can slide back and forth along the x–axis.

    (a) Find x as a function of θ (θ=angle POQ).
    (b) Assume the lengths are in centimeters and the angular speed,dθ/dt, is 2 radians persecond counter clockwise. Find the speed at which point Q is moving when θ =π/2 and when θ =π/4. Give units.

    2. Relevant equations

    3. The attempt at a solution

    Having a hard time understanding what to do for this problem.
  2. jcsd
  3. Oct 12, 2011 #2


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    'l' is fixed and 'a' is fixed. theta is variable. If theta=0 then x=l+a, if theta=(-pi) then x=l-a, right? You want to express x as function of theta. Use some trig, like the law of cosines.
  4. Oct 12, 2011 #3


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    Can you find x in terms of , a, and θ .

    Use the law of cosines.
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