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Homework Help: Bird's speed

  1. Nov 15, 2009 #1
    I attempted this problem, and got it wrong. I am a little lost on what I am doing wrong. Any help would be nice. It is due tonight.

    Problem: A 300 g bird flying along at 6.4 m/s sees a 10 g insect heading straight toward it with a speed of 33 m/s (as measured by an observer on the ground, not by the bird). The bird opens its mouth wide and enjoys a nice lunch. What is the bird's speed immediately after swallowing?

    For my wrong answer, I used the equation Vf = (MVi)/Mf, which game me ((.3 kg)(6.4 m/s))/.31 kg, which was wrong. (Lowercase letters should be subscripts)
  2. jcsd
  3. Nov 15, 2009 #2
    Consider the initial and final momentums and apply, as you already have the conservation of momentum.

    Make sure you consider everything in the system, the equation you posted is wrong in this situation.
  4. Nov 15, 2009 #3
    My next thought is that it doesn't change. The speed of the bird stays 6.4 m/s. But I am not sure if that is right either.
  5. Nov 15, 2009 #4
    I tried what I said, and it was wrong too, but I thought I would try anyways.

    When you say I have the initial and final momentums, how do you get the final and initial? Is the initial speed for the bird, which I would say it is?
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