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Homework Help: Uniform circular acceleration and direction

  1. Sep 19, 2008 #1
    1. The problem statement, all variables and given/known data
    Birds of prey rise up and down on thermals. A bird completes circle of radius 8m every 5s and rises vertically at a rate of 3.0 m/s. Assume uniform acceleration. Find

    a)speed of bird relative to ground
    b)magnitude of acceleration
    c)direction of birds acceleration
    d)angle between birds velocity vector and horizontal.

    2. Relevant equations

    3. The attempt at a solution

    I have found the answer to a be 10.5 m/s, the answer to b is 12.6 m/s^2

    c)at/ar=tan^-1(3/12.6)=13.3 degrees

    d) I'm not sure how to proceed for this equation.

    Any help is greatly appreciated and thank you for your time.
  2. jcsd
  3. Sep 19, 2008 #2


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    For part c the bird is in uniform circular motion. The bird is rising at a rate of 3m/s is not an acceleration.

    For part d you have the vertical component of velocity and the component tangent to the circular motion. Find the resultant.
  4. Sep 19, 2008 #3
    Thanl you very much sir for the help and I finally got d :). HOwever I'm still a little bit confused about c. Centripetal acceleration has the same magnitude but varying direction so how am I supposed to find the direction of the birds acceleration above the horizontal.
  5. Sep 19, 2008 #4


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    C says nothing about direction above the horizontal, it merely asks for direction as you have typed it.
  6. Sep 19, 2008 #5
    I see, thanks again.
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