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Thread: Physics Help

  1. October 6th 2012, 11:38 AM #1
    Louisana1
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    Physics Help

    A migrating bird is initially flying south at 7 m/s. To avoid hitting a high-rise building, the bird veers and changes its velocity to 6 m/s east over a period of 2 s. What is the bird's average acceleration (magnitude and direction) during this 2 s interval?
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  2. October 6th 2012, 01:37 PM #2
    ILikeSerena
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    Re: Physics Help

    Quote Originally Posted by Louisana1 View Post
    A migrating bird is initially flying south at 7 m/s. To avoid hitting a high-rise building, the bird veers and changes its velocity to 6 m/s east over a period of 2 s. What is the bird's average acceleration (magnitude and direction) during this 2 s interval?
    Hi Louisana1!

    Can you write the initial velocity as a vector?
    And the final velocity as a vector as well?

    If so, can you fill them in the formula for average accelation?
    That formula is:
    \vec a_{average} = {1 \over \Delta t} (\vec v_{final} - \vec v_{initial})
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  3. October 6th 2012, 04:18 PM #3
    Louisana1
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    Re: Physics Help

    -1/2
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  4. October 6th 2012, 04:52 PM #4
    skeeter
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    Re: Physics Help

    subtracting vectors ...

    i = unit vector in positive x-direction (East)

    j = unit vector in positive y-direction (North)

    v_0 = -7j

    v_f = 6i

    \Delta v = v_f - v_0 = 6i + 7j

    a = \frac{\Delta v}{\Delta t} = \frac{6i + 7j}{2} = 3i +3.5j

    |a| = \sqrt{3^2 + 3.5^2} = 4.6 \, m/s^2

    direction of the average acceleration vector ...

    \theta = \arctan\left(\frac{3.5}{3}\right) = 49^\circ
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  5. October 6th 2012, 06:05 PM #5
    Louisana1
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    Re: Physics Help

    not sure how you got the 49
    Thanks skeeter
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  6. October 6th 2012, 06:06 PM #6
    skeeter
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    Re: Physics Help

    the inverse tangent function on my calculator ...
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  7. October 6th 2012, 06:07 PM #7
    Louisana1
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    Re: Physics Help

    It said it was wrong on my online homework
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  8. October 6th 2012, 06:13 PM #8
    skeeter
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    Re: Physics Help

    Quote Originally Posted by Louisana1 View Post
    It said it was wrong on my online homework
    the angle is rounded to the nearest degree ... what is the criteria for entering answers as far as decimal places? If it's significant figures, it should be 50 degrees.
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  9. October 6th 2012, 06:16 PM #9
    Louisana1
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    Re: Physics Help

    still wrong I'm trying to figure it out too
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  10. October 6th 2012, 06:34 PM #10
    HallsofIvy
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    Re: Physics Help

    What was wrong? What answer did you give?
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  11. October 8th 2012, 04:37 PM #11
    Louisana1
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    Re: Physics Help

    the 49 degrees is incorrect the other part is right
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