physics

a stone falls from a cliff and travels 34.3m in the last second before it reaches the ground. calculate the height of the cliff.

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  1. Let T be the total time to fall.
    Let H be the cliff height.
    You must solve two equations in two unkonowns. No big deal.

    H = (1/2) g T^2
    H - 34.3 = (1/2) g (T-1)^2

    First eliminate H
    34.3 = (g/2)[T^2 - T^2 +2T -1]
    = (g/2)(2T-1)
    (2T-1) = 7.0 s
    T = 4.0 s

    Then solve for H. I get 78.4 m.

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  2. I didnt get it

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