Two solid spheres each of radius $R$ made of the same material are placed in contact with each other. If the gravitational force acting between them is $F$,then:

Six point masses of mass $m$ each are at the vertices of a regular hexagon of side $l$. Calculate the net gravitational force on any one of the masses.

$A$ mass $M$ is divided into two parts $xM$ and $(1 - x)M$. For what value of $x$ is the gravitational force between them maximum for a given distance?

Two identical spheres each of radius $r$ are placed in contact with each other. Show that the gravitational force between them is proportional to $r^4$.

Two masses $m_1$ and $m_2$ $(m_1 < m_2)$ are released from rest from a finite distance. They start moving under their mutual gravitational attraction.

Three particles each of mass $m_{1}$ are placed at the corners of an equilateral triangle of side $\frac{L}{3}$. $A$ particle of mass $m_{2}$ is placed at the midpoint of any one side of the triangle. Due to the system of particles,the net gravitational force acting on $m_{2}$ is ($G$ = Universal constant of gravitation).