Two particles, one heavy and the other light, placed at 50 cm from each other, are under the influence of gravitational force of one another. If mass of the heavier particle is 4 kg and its acceleration under the influence of gravitational force is $5 \times 10^{-10} \mathrm{~ms}^{-2}$, find the mass of the lighter particle.

Two spheres of masses $M_1$ and $M_2$ are in air separated by a distance of d m . The gravitational force of attraction between them is $F$. If the space around the masses is filled with a liquid of density $\rho$, the force between the masses will be

A body is projected vertically upwards from the surface of earth with a velocity ' $v$ ' to reach a height of $10 R$, where $R$ is the radius of the earth, then $v$ is