Question

A totally reflecting mirror (small $\&$ plane) is illuminated normally by parallel beam of light. The mass of the mirror is $50\text{g}.$ Find the power of the source need to support the weight of the mirror $(\text{Use}g=10{\text{ms}}^{-2})$

• A. $75\text{MW}$
• B. $100\text{MW}$
• C. $25\text{MW}$
• D. $1.25\text{MW}$

Answer 1

The correct option is A $75\text{MW}$

$\text{Given,}m=50\text{g};g=10{\text{ms}}^{-2}$

For a perfectly reflecting surface, the force exerted on the surface is,

$R.F=\frac{2IA}{c}$

The weight of the mirror is balanced.

i.e., $W=R.F$

$\Rightarrow mg=\frac{2P}{c}$

$\therefore P=\frac{mgc}{2}$

$=\frac{50\times {10}^{-3}\times 10\times 3\times {10}^8}{2}=75\times {10}^6\text{W}=75\text{MW}$

<!--td {border: 1px solid #ccc;}br {mso-data-placement:same-cell;}--> Hence, $\left(A\right)$ is the correct answer.