Solving for Cliff Height: An Alert Hiker's Task

[black_hole]

Homework Statement

An alert hiker sees a boulder fall from the top of a distant cliff and notes that it takes 1.3s for the boulder to fall the last 3rd of the way to the ground. Ignore air resistance.a) what is the height of the cliff in meters? b) If in part a) you get 2 solutions what does the extraneous one represent?

Homework Equations

The Attempt at a Solution

looking at the last 3rd
Vi = ?
Vf = 0 m/s
a = -9.8 m/s/s
t = 1.3s
x = ?

possibly going to use this equation: x = xo +vit +.5at^2 ?

 

[foonis]

you should use the equation y = yo +vit +.5gt^2 for vertical motion.
also Vi should equal zero, as the boulder begins from rest in the y-axis and Vf should equal the final velocity as the boulder hits the ground