# 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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