# Calculate acceleration due to gravity

#### rasen58

1. 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.

2. Homework Equations
Δy = v0t + 1/2 at2

3. 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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#### SammyS

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1. 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.

2. Homework Equations
Δy = v0t + 1/2 at2

3. 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

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Get used to facing problems/exercises in which people have swapped quantities/values to be found from the problem statement for other "given" values, and failed to correct answer keys.

#### rasen58

Okay, so I'm right. Thank you.