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This isn't really homework, but I'll be taking intro Physics in fall and am trying to get a grasp on the material ahead of time so I can do well.

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 to the last third of the way to the ground. You may ignore air resistance.

A. What is the heigh of the claff in meters?

What is wrong with how I did it described below, and why does the answer in the solution book say (2/3)h=(1/2)(g)(T - DeltaT)^2 with h being total height of the cliff, DeltaT being 1.3s, and T being the total time to hit the ground? Shouldn't it be (2/3)h=(1/2)(g)(DeltaT)^2

I thought: Amount fallen = (2/3)(Total height) = (1/2)(g)(t)^2

(Total height) = (3/2)(1/2)(g)(t)^2 = (3/2)(1/2)(9.8)(1.3)^2 = 12.4m

The solution they provide is the attached image.

## 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 to the last third of the way to the ground. You may ignore air resistance.

A. What is the heigh of the claff in meters?

## Homework Equations

What is wrong with how I did it described below, and why does the answer in the solution book say (2/3)h=(1/2)(g)(T - DeltaT)^2 with h being total height of the cliff, DeltaT being 1.3s, and T being the total time to hit the ground? Shouldn't it be (2/3)h=(1/2)(g)(DeltaT)^2

## The Attempt at a Solution

I thought: Amount fallen = (2/3)(Total height) = (1/2)(g)(t)^2

(Total height) = (3/2)(1/2)(g)(t)^2 = (3/2)(1/2)(9.8)(1.3)^2 = 12.4m

The solution they provide is the attached image.