Which of the following methods uses a rotary shaker?

Consider the following statements for $X = \dot{C}H_3$ and $Y = \dot{C}F_3$:
$(I)$ When $X$ dimerises,the bond angle decreases.
$(II)$ When $X$ dimerises,the bond angle increases.
$(III)$ In the $X-Y$ molecule,the $C-C$ bond length is less than that in the $Y-Y$ molecule.
$(IV)$ The bond angle in $X$ is greater than that in $Y$.

$A$ particle of mass $M$ is situated at the centre of a spherical shell of mass $M$ and radius $a$. The gravitational potential at a point situated at a distance of $\frac{a}{2}$ from the centre will be:

Which of the following types of cell junctions is not found in animal tissues?

Tubectomy is a method of sterilization in which

$A$ cannon ball is fired with a velocity $200\, m/s$ at an angle of $60^{\circ}$ with the horizontal. At the highest point of its flight,it explodes into $3$ equal fragments. One fragment goes vertically upwards with a velocity $100\, m/s$,and the second one falls vertically downwards with a velocity $100\, m/s$. What will be the velocity of the third fragment?