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## Homework Statement

A person does 115 J of work in throwing a 0.325 kg rock straight up into the air. How high will the rock get, assuming there is 20 J of air resistance?

## Homework Equations

From what I formulated: W =

**Δ**PE

The answer says E

_{1}= E

_{2}, but I think that's the exact same as the formula I used.

## The Attempt at a Solution

W =

**Δ**PE

115= mgh - 0

115 = (0.325)(9.8)h - 20

h = 42.386

It looked right in my head, but the problem is that the answer differ in the placement of the -20 J.

This is the correct answer given to me:

115 - 20 = E

_{p}

_{2}

95 = mgh

95 = (0.325)(9.8)h

h = 29.83

30 J (Significant figured)

I don't understand why the -20 J should be placed with the work being done (the left side of the equation). I appreciate any attempt at helping me understand the reason.