What is the acceleration due to gravity on Planet Plutnik?

[lovemake1]

Homework Statement

On Planet Plutnik the acceleration due to gravtiy is not 9.8m/s^2.
An object dropped is found to fall the final 15m of its trip in 2seconds.
It lands with a speed of 10m/s. Find the acceleration due to gravity on Planet Plutnik.

Homework Equations

d = vit + 1/2at^2
vf^2 = vi^2 + 2ad

The Attempt at a Solution

d = vit + 1/2 at^2

vi would be 0 in this case right?
and distance is 15m with final velocity 10m/s
vf^2 = vi^2 + 2ad
10^2 = 0 + 2a15
100 = 30a
a is 1/3 m/s^2 ?

 

[mgb_phys]

Not necessarily
It doesn't say it was dropped 15m, it says the final 15m of it's fall was 2s

You need to find what height it was dropped from.

 

[holezch]

I was just looking at this, we know that in the 15m of the fall (from 15m to 0m in 2 seconds) and the final velocity is 10 m/s. Since it is a free fall question, the acceleration is constant, so using the formula:

y = y0 + 1/2(V0 + V)t = 0 = 15 + 1/2(v0 + 10)2

solve for v0 then plug it into:

Vy^2 = Vy0^2 + 2a(x-x0) solve for a and you are done