The distance of an object from a spherical mirror is equal to the focal length of the mirror. Then the image:

If the distances of the object and its real image from the principal focus of a concave mirror are $16 \ cm$ and $9 \ cm$ respectively,then the focal length of the mirror is (in $cm$)

$A$ concave mirror for face viewing has a focal length of $0.4\,m$. The distance at which you hold the mirror from your face in order to see your image upright with a magnification of $5$ is......$m$.

$A$ thin rod of length $f/3$ lies along the axis of a concave mirror of focal length $f$. One end of its magnified image touches an end of the rod. The longitudinal magnification of the image is

Incident parallel rays make an angle of $5^{\circ}$ with the axis of a concave mirror of focal length $20 \ cm$. The perpendicular distance of the image from the axis is nearly $-$ (in $cm$)

$A$ concave mirror of focal length $f$ (in air) is immersed in water $(\mu = 4/3)$. The focal length of the mirror in water will be