# Calculate acceleration due to gravity

## Homework Statement

A stone is thrown horizontally from a cliff on a different planet with a speed of 10 m/s. The cliff has height 200m, and takes 4 s to hit the ground. Assume no air friction. What is the acceleration due to gravity on this planet.

## Homework Equations

Δy = v0t + 1/2 at2

## The Attempt at a Solution

I thought the initial vertical velocity would be 0 since it's thrown horizontally, so the first term of the equation disappears. And they give you t = 4, so I did 200*2/16 = 25 m/s^2.
But apparently the answer is 5 m/s^2.
Why?

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Bystander
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Why?
1/2 at2
One half "a" times "t" squared.

SammyS
Staff Emeritus
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Gold Member

## Homework Statement

A stone is thrown horizontally from a cliff on a different planet with a speed of 10 m/s. The cliff has height 200m, and takes 4 s to hit the ground. Assume no air friction. What is the acceleration due to gravity on this planet.

## Homework Equations

Δy = v0t + 1/2 at2

## The Attempt at a Solution

I thought the initial vertical velocity would be 0 since it's thrown horizontally, so the first term of the equation disappears. And they give you t = 4, so I did 200*2/16 = 25 m/s^2.
But apparently the answer is 5 m/s^2.
Why?

I agree it's 25 m/s2 .

Bystander