Question

A car has a convex mirror as its side mirror of focal length 30 cm.
A second car is 5m behind the first car. Find the position of the
second car as seen in the mirror of first car.​

Answer 1

Answer:

REF.Image

dt

du

=ϑ

0

=15ms

−1

We have,

focal length of the mirror (f)= +20 cm

object distance 'u' = -280 cm

and object velocity (

dt

du

)=15ms

−1

We know that,

ϑ

1

+

u

1

=

f

1

___ (i) (mirror formula)

Where, ϑ→ image distance.

ϑ

1

=

280

1

=

20

1

⇒

ϑ

1

=

20

1

+

280

1

=

280

15

⇒

ϑ

1

=

280

15

differentiating (i) with respect to time

ϑ

2

−1

dt

dϑ

−

u

2

1

dt

du

=0

⇒−

280

15

×

280

15

ϑ

i

=

280

1

×

280

1

×15

⇒ϑ

i

=

dt

du

=

15

1

ms

−1