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Homework Help: Find the speed of the bird relative to the ground

  1. Sep 17, 2007 #1
    1. The problem statement, all variables and given/known data

    It is common to see birds of prey rising upward on thermals. The paths they take may be spiral-like. You can model the spiral motion as uniform circular motion combined with a constant upward velocity. Assume a bird completes a circle of radius 8.00 every 5.00 and rises vertically at a rate of 3.00 .

    Find the speed of the bird relative to the ground.
    Find the magnitude of the bird's acceleration.
    Find the direction of the bird's acceleration.
    Find the angle between the bird's velocity vector and the horizontal.

    2. Relevant equations

    I used the relative velocity equation:

    vector velocity = vector v' + Vector V

    3. The attempt at a solution

    I plugged in

    vector velocity = 3 + (8/5) then I got the answer 4.6 m/s which is incorrect. I thought that this would be the right answer but its not.

    So since this is wrong, the other parts wouldn't work either.

    Thanks for helping!
  2. jcsd
  3. Sep 17, 2007 #2


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    Homework Helper

    I'm a little confused by "speed of the bird relative to ground"... are they asking for the rate at which the height is changing (in this case the answer is just 3.00m/s)... or are they asking for the speed relative to a fixed position on the ground?

    In the second case there are two components to the velocity... the vertical component and the horizontal component... The vertical component is 3.00m/s.

    What is the horizontal component? it isn't 8/5... what is the circumference of a circle?
  4. Sep 19, 2007 #3
    I have no idea what it is asking for? I tried the second case of your idea and it wasn't right also. Do you know if the equation that I used was correct?
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