State whether the following statement is True or False:
The inertia of an object depends upon its mass.

$(a)$ Write the formula to find the magnitude of the gravitational force between the Earth and an object on the surface of the Earth.
$(b)$ What is the direction of acceleration due to gravity?

When a spaceship is two earth radii distant from the centre of the earth,its gravitational acceleration is: (in $, m s^{-2}$)

The mass of a girl is $50\, kg$. What will be her approximate weight on the Earth? How will her mass and weight change on the surface of the Moon?

Find the weight of an $80\, kg$ man on the surface of the moon. What would be his mass on the Earth and on the moon? $(g_{e} = 9.8\, m s^{-2}, g_{m} = 1.63\, m s^{-2})$

What is the ratio of the gravitational force between two masses kept at a certain distance in air to the force between them when kept in any other medium?