physics
posted by Anonymous .
A rock is thrown vertically upward from the edge of a cliff. The rock reaches a maximum height of 20.6 m above the top of the cliff before falling to the base of the cliff, landing 6.54 s after it was thrown. How high is the cliff?

physics 
Henry
V^2 = Vo^2 + 2g*d.
Vo^2 = V^22g*d
Vo^2 = 0  (19.6)*20.6 = 403.76
Vo = 20.1 m/s. = Initial velocity.
V = Vo + g*t.
Tr = (VVo)/g = (020.1)/9.8 = 2.05 s.
= Rise time.
Tr + Tf = 6.54 s.
2.05 + Tf = 6.54
Tf = 6.54  2.05 = 4.49 s. = Fall time
from 20.6 m above the cliff to Gnd.
Vo*t + 0.5g*t^2 = 20.6 + h.
0 + 4.9t^2 = 20.6 + h
h = 4.9*(4.49)^2  20.6 = 78.2 m.
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