Force of gravitation between two masses is found to be $F$ in vacuum. If both the masses are dipped in water at same distance then, new force will be

Two point masses $m$ and $4$ $m$ are separated by a distance $d$ on a line. A third point mass $m_0$ is to be placed at a point on the line such that the net gravitational force on it is zero.

The distance of that point from the $m$ mass is

A large number of identical point masses $m$ are placed along $x$-axis, at $x=0, 1, 2, 4, .....$ The magnitude of gravitational force on mass at origin $(x=0),$ will be

Three particles $A,$ $B$ and $C$ each of mass $m$ are lying at the corners of an equilateral triangle of side $L.$ If the particle $A$ is released keeping the particles $B$ and $C$ fixed, the magnitude of instantaneous acceleration of $A$ is