A double star system consists of two stars $A$ and $B$ which have time period $T_A$ and $T_B.$ Radius $R_A$ and $R_B$ and mass $M_A$ and $M_B$. Choose the correct option.

Mass $M$ is uniformly distributed only on the curved surface of a thin hemispherical shell. $A, B$ and $C$ are three points on the circular base of the hemisphere, such that $A$ is the centre. Let the gravitational potential at points $A, B$ and $C$ be $V_A,V_B,V_C$ respectively. Then

Assertion: In free space, a uniform spherical planet of mass $M$ has a smooth narrow tunnel along its diameter. This planet and another super-dense small particle of mass $M$ start approaching towards each other from rest under the action of their gravitational forces. When the particle passes through the centre of the planet, the sum of kinetic energies of both the bodies is maximum.

Reason: When the resultant of all forces acting on a particle or a particle like object (initially, at rest) is constant in direction, the kinetic energy of the particle keeps on increasing.

Assertion: If the earth suddenly stops rotating about its axis, then the value of effective acceleration due to gravity $\left(g_{\mathrm{effective}}\right)$ will become the same at all the places. (Assume earth to be spherical)

Reason: The value of effective acceleration due to gravity $\left(g_{\mathrm{effective}}\right)$ is independent of the rotation of the earth.

Assertion: Gravitational potential of the earth at every place on its is negative. (taking potential at infinity to be zero)

Reason: Everybody on earth is bound by the attraction of earth.

The figure shows elliptical orbit of a planet $m$ about the sun $S$. The shaded area $SCD$ is twice the shaded area $SAB$. If $t_1$ is the time for the planet to move from $C$ to $D$ and $t_2$ is the time to move from $A$ to $B$, then: