Question

Image of an object approaching a convex mirror of radius of curvature $20\, m$ along its optical axis is observed to move from $\frac{25}{3} m$ to $\frac{50}{7} m$ in $30$ seconds. What is the speed of the object in $km$ per hour?

Answer 1

For $v_{1}=\frac{50}{7}\, m ,$
$ u _{1}=-25\, m$
$v _{2}=\frac{25}{3} \,m , $
$u _{2}=-50\, m$
Speed of object $=\frac{25}{30} \times \frac{18}{5}=3\, kmph$