Question

a object moving is toward the concave mirrorof focal length 24cm. when it is at a distance of 60 cm from the mirror,its speed is 9cm/s .the speed of its image at that instant ,is​

Answer 1

Answer:

Given that,

Focal length f=24cm

Distance from the mirroru=60cm

Now, by using mirror formula,

1/f = 1/v + 1/u.....(I)

1/24 = 1/v + 1/16,

1/v = 1/40.

v = 40 cm.

Now, on differentiating of equation (I)

1/f = 1/v + 1/u.

1 dv 1. du

0 = ---------- - ------------

v² dt u² dt.

v². du

dv/dt = ––––––––––

u² dt

-40 × 40

dv/dt= ––————– × 9.

60 × 60.

= -4 cm/s.

Negative sign indicate that the velocity of the image is away from the mirror

Negative sign indicate that the velocity of the image is away from the mirrorHence, the velocity of the image is 4 cm/s.

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