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14 May, 03:37

A 72-kg boy is surfing and catches a wave which gives him an initial speed of 1.6 m/s. He then drops through a height of 1.61 m, and ends with a speed of 8.5 m/s. How much nonconservative work (in kJ) was done on the boy

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  1. 14 May, 06:50
    0
    2849.98 J

    Explanation:

    From the question,

    Work done by the boy = change Potential energy of the boy + change in kinetic energy of the boy

    W = ΔP + ΔK ... Equation 1

    Where W = work done by the boy, ΔP = change in potential energy of the boy, ΔK = Change in kinetic energy of the boy.

    But,

    ΔP = mgΔh ... Equation 2

    ΔK = 1/2mΔv² ... Equation 3

    Where m = mass of the boy, Δh = change in height of the boy, Δv = change in velocity of the boy.

    Substitute equation 2 and 3 into equation 1

    W = mgΔh+1/2mΔv² ... Equation 4

    Given: m = 72 kg, Δh = 1.61 m, Δv = 8.5-1.6 = 6.9 m/s, g = 9.8 m/s²

    Substitute into equation 4

    W = 72 (9.8) (1.61) + 1/2 (72) (6.9²)

    W = 1136.016+1713.96

    W = 2849.98 J
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