Question

an object is placed at the distance of 40 cm from a concave mirror of focal length 15 CM if the object is displaced through a distance of 20 CM towards the mirror by how much distance is the image displaced

Answer 1

hey dear your ans is here..
first using mirror formula
1/u+1/v=1/f
f=-15
u=-40

find v

now for u=-20
find v
now take difference of it so you will get answer

Answer 2

mirror: concave

f = -15 cm

u = -40 cm

with this information, find v

1/f = 1/v + 1/u

1/v = 1/f - 1/u

-1/15 + 1/40 = -1/24

therefore, v = -24 cm

now, object is displaced by 20 cm.

therefore, -40 -(-20)

= -20 cm

u = -20 cm

f = -15 cm

now find v using the above data

1/v = 1/f - 1/u

= -1/15 + 1/20

= -1/60

therefore, v = -60 cm

now take the difference to know the displacement of the image:

that is, -60 - (-24)

= -36 cm is the displacement of the image.