Question

Find the image velocity in the given diagram.

Answer 1

From lens formula,

$\frac{1}{v}-\frac{1}{u}=\frac{1}{f}$

Substituting the data given in the question,

$\frac{1}{v}-\frac{1}{(-30)}=\frac{1}{20}\Rightarrow v=60\text{cm}$

$m=\frac{v}{u}=-2$


As we know,

${\overrightarrow{v}}_{IL}=m^2{\overrightarrow{v}}_{OL}$

$\Rightarrow [v_I-(-2\left)\right]=4[6-(-2\left)\right]$

$\Rightarrow v_I+2=4\times 8\Rightarrow v_I=30{\text{ms}}^{-1}$

Hence, option (b) is the correct answer.