1.

A convex driving mirror of focal length 20cm, is fitted in a motor car. If the second car 2m broad and 1.6m hight is 6m away from first car and overtake the first car at a relative speed of 15m//s, then how fast will the image he moving?

Answer»

`0.016m//s`
`0.0257m//s`
`0.162cm`
`0.0073m//s`

Solution :(a) Mirror formula `1/V+1/u=1/f`
Differentiating w.r.t we get
`0=-1/(v^(2))(DV)/(DT)-1/(u^(2))(du)/(dt)`
`(du)/(dt)=-(v^(2))/(u^(2))(du)/(dt)`
But `(du)/(dt)=15m//s`
Now `1/v=(1/20+1/600)`
`:.v=600-31cm` and `v/u=(600/31)/600=1/31`
`:.` SPEED of image `=(dv)/(dt)=-(1/31)^(2)xx16=0.016m//s`


Discussion

No Comment Found

Related InterviewSolutions