Calculate the force of gravitation between the earth and the Sun, given that the mass of the earth $= 6 \times 10^{24}\, kg$ and of the Sun $= 2 \times 10^{30}\, kg$. The average distance between the two is $1.5 \times 10^{11}\, m$.

A stone is allowed to fall from the top of a tower $100\, m$ high and at the same time another stone is projected vertically upwards from the ground with a velocity of $25\, m/s$. Calculate when and where the two stones will meet.

Gravitational force on the surface of the moon is only $\frac {1} {6}$ as strong as gravitational force on the earth. What is the weight in newtons of a $10\, kg$ object on the moon and on the earth?

Why does an object float or sink when placed on the surface of water?

State the universal law of gravitation.