A car is fitted with a convex side-view mirror of focal length 20 cm. A second car 2.8m behind the first car is overtaking the first car at a relative speed of 15 `m/s`. The speed of the image of the second car as seen in the mrror of the first one is:

Options

A. `(1)/(15)m//s`
B. `10m//s`
C. `15m//s`
D. `(1)/(10)m//s`

Answer

A

Explanation

From mirror formula
`(1)/(v)+(1)/(u)=(1)/(f)" so, "(dv)/(dt)=-(v^(2))/(u^(2))((du)/(dt))`
`rArr (dv)/(dt)=-((f)/(u-f))^(2)(du)/(dt) rArr (dv)/(dt)=(1)/(15)m//s`