Who discovered the four largest moons of Jupiter, now known as the Galilean moons?

Three identical spherical shells, each of mass $m$ and radius $r$ are placed as shown in the figure. Consider an axis $X{X}^{\mathit{\prime }}$ which is touching the two shells and passing through the diameter of the third shell. The moment of inertia of the system consisting of these three spherical shells about $X{X}^{\mathit{\prime }}$ axis is:

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R

Assertion A : An electric fan continues to rotate for some time after the current is switched off.

Reason R: Fan continues to rotate due to inertia of motion.

In the light of above statements, choose the most appropriate answer from the options given below.

Two artificial satellites $A$ and $B$ are at a distance $r_{\mathrm{A}}$ and $r_{\mathrm{B}}$ above the earth's surface, respectively. If the radius of earth is $R$, then the ratio of their speeds will be

Two satellites $A$ and $B$ move round the earth in the same orbit. The mass of $B$ is twice the mass of $A$. Which of the following statement is true?