Question

When an object is kept at a distance of $30\text{cm}$ from a concave mirror, the image is formed at a distance of $10\text{cm}$. If the object is moved with a speed of $9{\text{cms}}^{-1}$ in horizontal direction, the speed with which the image moves is

• A. $0.1\text{cm/s}$
• B. $1\text{cm/s}$
• C. $3\text{cm/s}$
• D. $9\text{cm/s}$

Answer 1

The correct option is B $1\text{cm/s}$

Relation between the image and object speed,
$v_i=-{\left(\frac{v}{u}\right)}^2{v}_0$
$=-{\left(\frac{-10}{-30}\right)}^{2}9$
$=-1cm/s$