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**1. Homework Statement**

A rock is thrown downward from an unknown height above the ground with an initial speed

of 27 m/s. It strikes the ground 7.1 s later. Determine the initial height of the rock above the ground. The acceleration of gravity is 9.8 m/s

^{2}. Answer in units of m.

**2. Homework Equations**

[itex]\Delta[/itex]x = v

_{i}t + 1/2 at

^{2}

**3. The Attempt at a Solution**

I'm not sure if this equation is correct, first of all, but it has all of the variables given in the problem. I don't know how to deal with the fact that it's

*thrown*down, but I thought the v

_{i}would take care of it.

We have acceleration, initial velocity, and time, and the equation solves for displacement. What am I doing wrong? How should this problem be set up differently and why?

Thank you very much.