Calculating Gravity Acceleration on Planet Zog

[Punchlinegirl]

On planet Zog, Mr Spock measures that it takes 1.41 s for a mass of 0.3 kg to hit the ground when released from rest from a height of 3.09m. Calculate the size of acceleration of gravity on that planet.
I know that a= GM/r^2, but I don't know the radius. Any suggestions on where to begin?

 

[Berislav]

Any suggestions on where to begin?

Assuming that the height from which the mass is dropped is negligable compared to the radius, this is a trick question.

 

[Jameson]

I don't believe you need to use the equation you gave. Use a simple kinematic equation.

$$d = v_{i}t + \frac{1}{2}at^2$$

You know d, vi, and t. Solve for a.

EDIT: Maybe this won't work, but it seems right to me. The mass shouldn't matter, as everything accelerates at he same rate, regardless of mass.