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March 29, 2017

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1) The velocity of a diver just before hitting the water is -11.8 m/s, where the minus sign indicates that her motion is directly downward. What is her displacement during the last 1.06 s of the dive?

I know that the formula for displacement is deltaX= x - x0. Would I do -11.8 - 1.06?

  • Physics(Please help) - ,

    Use the acceleration of gravity to find her velocity 1.2 s before impact. Average the two velocities times the 1.2 s to get the displacement.

    v = v0 - g*t
    -10.4 = v0 - 9.81*1.2
    v0 = 1.372

    So the diver was above the level from which she dove from at 1.2 s before impact. The time of max height can be found by using v0 = 0 in the above equation.
    t = v/g = 10.4/9.81 = 1.06 s

    So max height was reached 1.06 seconds before impact.

    Vavg = (1.372 - 10.4)/2
    Vavg = -4.514

    Displacement = Vavg*1.2 = -5.4 m

    So her displacement during the last 1.2 s of the dive is 5.4 meters. Displacement is just the distance from starting point to finishing point regardless of the path taken. In this case her initial motion was upward to max height and then downward to the water. But the positive distance upward is irrelevant to the displacement in this case.

  • Physics(Please help) - ,

    For some reason when i put in 5.4 as the answer it said I was incorrect. I do not know why.

  • Physics(Please help) - ,

    The diver’s motion is free fall.
    Therefore
    h =g•t²/2
    v=g•t
    The speed 11.8 m/s was gained for the time
    t = v/g = 11.8/9.8 = 1.2 s.
    The height from which the diver janped was
    h = g•t²/2 =9.8•1.2²/2 = 7.1 m.
    The time for the first part covering is
    t1= 1.2 - 1.06 =0.14 s.
    The distance for this time is
    h1 = g•t1²/2 = 9.8•0.14²/2 = 0.1 m.
    Δh =7.1 -0.1 = 7 m

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