# One-Dimensional Motion with Constant Acceleration

## Homework Statement

A rock is released from rest from the top of a very high cliff, and accelerates downward at g.
Approximately how far does the rock travel in the first 7 seconds of its free-fall? (Assume no air friction.)

X=Xo+VoT+1/2AT^2

## The Attempt at a Solution

I understand how to work out the problem, but I do not know why it works. You simply substitute the numbers in to get the distance. But for some reason, you are not given (nor do you use) initial position like the equation calls for. Can someone explain why it's simply thrown away? The initial position can't be 0, as it's being dropped from a mountain.[/B]

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## Homework Statement

A rock is released from rest from the top of a very high cliff, and accelerates downward at g.
Approximately how far does the rock travel in the first 7 seconds of its free-fall? (Assume no air friction.)

X=Xo+VoT+1/2AT^2

## The Attempt at a Solution

I understand how to work out the problem, but I do not know why it works. You simply substitute the numbers in to get the distance. But for some reason, you are not given (nor do you use) initial position like the equation calls for. Can someone explain why it's simply thrown away? The initial position can't be 0, as it's being dropped from a mountain.[/B]
The question is asking how far the rock travels. That's the difference between the final position and the initial position. ##x_0## cancels when you take the difference.

HallsofIvy