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Circular Motion Question

  1. Mar 31, 2013 #1
    1. The problem statement, all variables and given/known data

    A bird of mass 0.5kg dives and then pulls out of the dive by flying in a portion of a vertical circle of radius 15m. At the bottom of the arc the birds speed is 25m/s.
    a) What is the magnitude of the net vertical force acting on the bird?
    b) What is the magnitude of the upward lift exerted on the bird by the air?

    2. Relevant equations

    Only give equations F=ma and a=[itex]\frac{v^2}{r}[/itex]

    3. The attempt at a solution

    So for (a) I got:
    a=[itex]\frac{v^2}{r}[/itex]
    =[itex]\frac{25^2}{15}[/itex]
    = 41.667m/s

    F=(ma) + (mg)
    = (0.5 x 41.667) + (0.5 x 9.8)
    = 25.7N

    Which I think also means that (b) is 20.8N (from F=ma)

    However a friend got the answer to (a) as 20.8N (she couldn't figure out (b))
     
  2. jcsd
  3. Mar 31, 2013 #2

    mukundpa

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    I think net vertical force will create a net vertical acceleration. What is (net?) vertical acceleration of the bird at the lowest point?
     
  4. Apr 1, 2013 #3

    haruspex

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    Using mukundpa's hint, you should get the right answer for (a). But you calculation from there to part (b) is also wrong. think about the directions of the two accelerations, a and g.
     
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