State any two properties of gravitational force.

$A$ stone is dropped from the roof of a building. It takes $4 \, s$ to reach the ground. Find the height of the building. $(g = 9.8 \, m \, s^{-2})$

Prove that if a body is thrown vertically upwards,then the time of ascent is equal to the time of descent.

$(i)$ Is the acceleration due to gravity of earth '$g$' always a constant at every place? Discuss.
$(ii)$ During a free fall,will heavier objects accelerate more than lighter ones? Give reason for your answer.

The graph below shows the change of ice to steam. Observe the change of state from ice to water and water to steam,and write two inferences that can be drawn from this graph about these changes of state.

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