Kepler's second law regarding the constancy of areal velocity of a planet is a consequence of the law of conservation of

Assertion $(A)$: Angular speed,linear speed,and kinetic energy change with time,but angular momentum remains constant for a planet orbiting the sun.
Reason $(R)$: Angular momentum is constant as no external torque acts on the planet.

If $A$ is the areal velocity of a planet of mass $M$,its angular momentum is

The figure shows the elliptical path $abcd$ of a planet around the sun $S$ such that the area of triangle $csa$ is $\frac{1}{4}$ of the area of the ellipse. With $db$ as the major axis and $ca$ as a chord perpendicular to the major axis,if $t_1$ is the time taken for the planet to travel along the path $abc$ and $t_2$ is the time taken for the path $cda$,then:

The mean radius of the earth's orbit around the sun is $1.5 \times 10^{11} \ m$. The mean radius of the orbit of mercury around the sun is $6 \times 10^{10} \ m$. The mercury will rotate around the sun in

The time period of a satellite of Earth is $24 \text{ hours}$. If the separation between the Earth and the satellite is decreased to one-fourth of the previous value, then its new time period will become: (in $\text{ hours}$)