Question from my school assignment :

A car is fitted with a convex mirror of focal length 20cm.A second car is 6m away from this mirror.The latter starts overtaking with a relative velocity of 15m/s.How fast does the image move and in which direction?

Is the answer 0.14m/s?

Kindly give full solution..

Rates assured :-)

I  differentiated and got 0.015m/s..yours comes to 0.017m/s

or is there some mistake in my differentiation?

1/f=1/u+1/v

Differentiating wrt distance,

0=(du/dx)(-1/u^2)-(dv/dx)(1/v^2)

So

(dv/dx)(1/v^2)--15/u^2

dv/dx=-15*(v/u)^2

       = -15(0.19/6)^2

          =0.015m/s

My initial answer was 0.014...by mistake typed it as 0.14..

anyway,did i make a mistake somewhere?

Thanks!:-)

Ok thanks guys...

The basic method is correct,right..I guess 0.015 and 0.017 difference can be neglected..

Thanks again!!