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6 January, 11:49

Sandra throws an object straight up into the air with an initial velocity of 38 ft/s from a platform that is 30 ft above the ground. Use the formula h (t) = -16t2+v0t+h0, where v0 is the initial velocity and h0 is the initial height. How long will it take for the object to hit the ground?

A. 1 s

B. 2 s

C. 3 s

D. 4 s

+5
Answers (1)
  1. 6 January, 11:57
    0
    The answer is C.

    Step-by-step explanation:

    Given formula h (t) = -16t2+v0t+h0, where v0 is the initial velocity and h0 is the initial height.

    In this case, the initial postion is a platform 30ft above ground so h0=+30

    The initial velocity is 38 ft/s straight up into the air so v0=+38

    h (t) = -16t2+38t+30

    When the object hits the ground, h=0.

    h=-16t2+38t+30=0

    Simplifying 8t2-19t-15=0

    (8t+5) (t-3) = 0

    t=-5/8 or 3

    As time cannot be - ve, t=3s. The answer is C.
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