Question

A particle is dropped to move along the axis of a concave mirror

Answer 1

$\huge\mathfrak\red{Heya\:..!}$

Distance of Image formed in the mirror is same as the distance of the object formed the surface of the mirror.

Thus is distance of object = u

Then distance of image = -u (as the image is formed at other side of the mirror)

Thus distance between image and object = 2u ...(1)

Now if mirror is approaching you/object with speed v, then distance travelled by mirror in unit time = v units

Thus distance between mirror and object in unit time = u - v

Thus distance between object and its image = 2(u-v)....(2)

From equations (1) and (2) distance between image and object is reduced by 2v units in unit time(1 second)

Thus speed of image w.r.t object = 2v

Answer 2

$\huge\mathfrak\red{AnSweR}$

Distance of Image formed in the mirror is same as the distance of the object formed the surface of the mirror.

Thus is distance of object = u

Then distance of image = -u (as the image is formed at other side of the mirror)

Thus distance between image and object = 2u ...(1)

Now if mirror is approaching you/object with speed v, then distance travelled by mirror in unit time = v units

Thus distance between mirror and object in unit time = u - v

Thus distance between object and its image = 2(u-v)....(2)

From equations (1) and (2) distance between image and object is reduced by 2v units in unit time(1 second)

Thus speed of image w.r.t object = 2v