Physics - Modern Physics Question with Solution | TestHub

Momentum $p=\frac{\mathrm{Energy}\left(\mathrm{E}\right)}{\mathrm{Speed} \mathrm{of} \mathrm{light}\left(\mathrm{c}\right)}$

$=\frac{\mathrm{Power}\times \mathrm{time}}{c}$

$=\frac{\left(20\times {10}^{-3}\mathrm{W}\right)\left(300\times {10}^{-9}\mathrm{s}\right)}{3\times {10}^8 \mathrm{m} {\mathrm{s}}^{-1}}$

$=2\times {10}^{-17} \mathrm{kg} \mathrm{m} {\mathrm{s}}^{-1}$

As momentum is conserved, therefore momentum of object will be $2\times {10}^{-17} \mathrm{kg} \mathrm{m} {\mathrm{s}}^{-1}$.