A solid sphere of mass $M$ and radius $R$ is divided into two unequal parts. The smaller part having mass $M / 8$ is converted into a sphere of radius $r$ and the larger part is converted into a circular disc of thickness $t$ and radius $2 R$. If $I_1$ is moment of inertia of a sphere having radius $r$ about an axis through its centre and $I_2$ is the moment of inertia of a disc about its diameter, the ratio of their moment of inertia $I_2 / I_1=$ $\_\_\_\_$

The position of an object having mass 0.1 kg as a function of time $t$ is given as

$\vec{r} = \left( 10 t^2 \hat{i} + 5 t^3 \hat{j} \right)$ m. At $t = 1$ s, which of the following statements are correct?

A. The linear momentum $\vec{p} = \left( 2 \hat{i} + 1.5 \hat{j} \right)$ kg·m/s.

B. The force acting on the object $\vec{F} = \left( 2 \hat{i} + 3 \hat{j} \right)$ N.

C. The angular momentum of the object about its origin $\vec{L} = 15 \hat{k}$ J·s.

D. The torque acting on the object about its origin $\vec{\tau} = 20 \hat{k}$ N·m.

Choose the correct answer from the options given below:

When the position vector $\vec{r} = x\hat{i} + y\hat{j} + z\hat{k}$ changes sign as $-\vec{r}$, which one of the following vector will not flip under sign change?

Two circular discs of radius each 10 cm are joined at their centres by a rod of length 30 cm and mass 600 gm as shown in figure.

If the mass of each disc is 600 gm and applied torque between two discs is $43 \times 10^5$ dyne.cm, the angular acceleration of the discs about the given axis $A B$ is $\_\_\_\_$ $\mathrm{rad} / \mathrm{s}^2$.