What should be the angle between two plane mirrors so that whatever be the angle of incidence,the incident ray and the reflected ray from the two mirrors are parallel to each other (in $^o$)?

$A$ ray of light is incident on a plane mirror at rest. The mirror starts turning at a uniform angular acceleration of $4\pi \, rad/s^2$. The reflected ray at the end of $\frac{1}{4} \, s$ must have turned through......$^o$

When a beam of light is incident on a plane mirror,it is found that a real image is formed. The incident beam must be

$A$ man runs towards a plane mirror at a speed of $15 \, m/s$. The speed of the image relative to the man is $...... \, m/s$.

$A$ point object is placed mid-way between two plane mirrors at a distance $a$ apart. The plane mirrors form an infinite number of images due to multiple reflections. The distance between the $n^{th}$ order images formed in the two mirrors is

Two plane mirrors are inclined to one another at an angle of $60^o$. $A$ ray is incident on mirror $M_1$ at an angle $i$. The reflected ray from mirror $M_1$ is shown in the figure. The angle of incidence $i$ is (in $^o$)