'''
In this exercise we write a function to calculate the gravitational force. 
Gravitational force is given by the following formula:
F_g = (G * m_1 * m_2) / r^2

Exercise A: 
Imagine we want to make a function which calculates the gravity on Earth.
Let's call this funcion `gravity_earth`.
Which of the variables become constants and which should be input parameters?

Hint: You will need to Google to find the required constant values for this 
function.
'''

# Your code here


'''
Exercise B:
Apply your function (`gravity_earth`) to calculate gravitational force on an 
object with mass of 10 kg. 

Solution should be 98.1 N.
'''

m = 10 # kg

# Your code here


'''
Exercise C:
Imagine we want to compare the gravitational force an astronaut experiences on 
different planets. Given that the astronaut weighs 90 kg, write a function 
which calculates the gravitational force on the astronaut on different planets.
'''

# Your code here