Calculate acceleration due to gravity

[rasen58]

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?

 

[Bystander]

Why?

1/2 at2

One half "a" times "t" squared.

 

[SammyS]

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?

Your answer (as well as your analysis) looks good to me !

I agree it's 25 m/s² .

 

[Bystander]

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.