Question

The earth receives energy from the sun at the rate of $1400{\text{Wm}}^{-2}.$ The force exerted by the solar radiation on the roof of dimensions $(16\text{m}\times 10\text{m})$ is nearly equal to-
$($Assume absorption coefficient of roof is $0.8)$

• A. $7.5\times {10}^{-4}\text{N}$
• B. $9\times {10}^{-4}\text{N}$
• C. $7.5\times {10}^{-2}\text{N}$
• D. $0.09\text{N}$

Answer 1

The correct option is B $9\times {10}^{-4}\text{N}$

Given,

$P=1400{\text{Wm}}^{-2};A=160{\text{m}}^2$

$\alpha =0.8\Rightarrow r=1-\alpha =1-0.8=0.2$

For a partially absorbing surface, the force exerted by the radiation is,

$F=\frac{IA}{c}(1+r)$

$F=\frac{1400\times 160}{3\times {10}^8}\times (1+0.2)$

$F=9\times {10}^{-4}\text{N}$

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