Question

The ratio of the speed of an object to the speed of its real image of magnification $m$ of a convex mirror is

• A. $-\frac{1}{m^2}$
• B. $m^2$
• C. $-m$
• D. $\frac{1}{m}$

Answer 1

Answer: (A)

$\frac{1}{u}+\frac{1}{v}=\frac{1}{f}$
$-\frac{1}{u^2}\frac{du}{dt}-\frac{1}{v^2}\frac{dv}{dt}=0$
$=-\frac{1}{u^2}{u}_0-\frac{1}{v^2}{v}_0=0$
$\frac{u_0}{v_0}=-\frac{u^2}{v^2}=-\frac{1}{m^2}$