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Math Help - physics acceleration

  1. #1
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    physics acceleration

    A fox is chasing a bunny. The bunny is initially hopping east at 9 m/s when it first sees the fox. Over the next half second the bunny changes its velocity to west at 13 m/s and escapes. What was the bunny's average acceleration (magnitude and direction) during this half-second interval?

    ______________m/s2

    What equation is used and how is this set up?
    I've tried drawing this and I have figured out 22m/s2
    and he is heading west but the 22 was wrong do I need to do something
    with the half second?

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  2. #2
    MHF Contributor MarkFL's Avatar
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    Re: physics acceleration

    I would let due east be the positive axis of motion, hence:

    \bar{a}=\frac{\Delta v}{\Delta t} where:

    \Delta v=v_f-v_i=-13\frac{\text{m}}{\text{s}}-9\frac{\text{m}}{\text{s}}

    \Delta t=\frac{1}{2}\text{s}
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  3. #3
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    Re: physics acceleration

    \vec{a} = \frac{\vec{v_f} - \vec{v_i}}{\Delta{t}}.

    If we set up our coordinate system such that east is positive and west is negative, then

    \vec{a} = \frac{-13 \frac{m}{s} - (9 \frac{m}{s})}{\frac{1}{2} s} = -44 \frac{m}{s^2}. The - sign indicates that the bunny is accelerating west.
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    Re: physics acceleration

    I've input -22 and -44 and both were incorrect. Thanks guys I'm still working at it
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  5. #5
    MHF Contributor MarkFL's Avatar
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    Re: physics acceleration

    If you are asked for the magnitude and direction, then the magnitude of the average acceleration is 44 m/sē and the direction is west.
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