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24 April, 17:26

The specialty of an athlete on the women's track team is the pole vault. She has a mass of 48 kg and her approach speed is 8.9 m/s. When she is directly above the bar, her speed is 1.6 m/s. Neglecting air resistance and any energy absorbed by the pole, determine the amount (in m) she has raised herself as she crosses the bar.

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  1. 24 April, 17:42
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    H = 3.9 m

    Explanation:

    mass (m) = 48 kg

    initial velocity (initial speed) (U) = 8.9 m/s

    final velocity (V) = 1.6 m/s

    acceleration due to gravity (g) = 9.8 m/s^{2}

    find the height she raised her self to as she crosses the bar (H)

    from energy conservation, the change in kinetic energy = change in potential energy

    0.5m (V^{2} - [test]U^{2}[/tex]) = mg (H-h)

    where h = initial height = 0 since she was on the ground

    the equation becomes

    0.5m (V^{2} - [test]U^{2}[/tex]) = mgH

    0.5 x 48 x (1.6^{2} - [test]8.9^{2}[/tex]) = 48 x 9.8 x H

    -1839.6 = 470.4 H (the negative sign indicates a decrease in kinetic energy so we would not be making use of it further)

    H = 3.9 m
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