Please help with the following question:

You are on a planet whose radius is known to be about 4500 km. You then perform the following experiment: You drop a rock from a height of 10.0 m and measure the time of its fall to be 2.65 s. What is the mass of the planet?

what equations can I use to solve this question and how can the time it took for the rock to fall be incorporated into this?

1 answer

d = 1/2 a t^2

10.0 * 2 = a * 2.65^2

calculate the gravitational acceleration (a)
... f = m a
... f / m = a

f = M * m * G / r^2
... f / m = M * G / r^2
... a = M * G / r^2

M is the planet's mass

G is the universal gravitation constant

r is the planets radius (in meters)