Your spaceship lands on an unknown planet. To determine the characteristics of this planet, you drop a wrench from 4.50 m above the ground and measure that it hits the ground 0.809 s later. Assuming that the planet has the same density as that of earth (5500 kg/m3), what is the radius of the planet?

Explanation:

First we need to find the acceleration due to gravity on the planet. The wrench took 0.809 s to fall from a height of 4.50 m so we can use the equation

Solving for g, we get

Recall that the acceleration due to gravity on a planet's surface can be written as

We can express the mass of the planet in terms of its density as follows:

The expression for g then becomes

Solving for we get

i think the answer is a, hope this is right, that would be my best guess.