1. Radiation pressure on a non-reflecting surface

For a perfectly absorbing (non-reflecting) surface at normal incidence,

$P = \frac{I}{c}$

where:

• $P$ = radiation pressure
• $I$ = intensity (energy flux)
• $c$ = speed of light

Force on area $A$ is:

$F = PA = \frac{IA}{c}$

So,

$A = \frac{Fc}{I}$

2. Given data

• Force: $F = 2.4 \times 10^{-4}\,\text{N}$
• Intensity: $I = 360\,\text{W/cm}^2$

Convert intensity into $\text{W/m}^2$:

$1\,\text{cm}^2 = 10^{-4}\,\text{m}^2$

Hence,

$360\,\text{W/cm}^2 = 360 \times 10^4\,\text{W/m}^2 = 3.6 \times 10^6\,\text{W/m}^2$

Also,

$c = 3 \times 10^8\,\text{m/s}$

3. Calculate area

Using

$A = \frac{Fc}{I}$

Substitute the values:

$A = \frac{(2.4 \times 10^{-4})(3 \times 10^8)}{3.6 \times 10^6}$

First calculate numerator:

$(2.4 \times 10^{-4})(3 \times 10^8) = 7.2 \times 10^4$

So,

$A = \frac{7.2 \times 10^4}{3.6 \times 10^6}$

$A = 2 \times 10^{-2}\,\text{m}^2$

$A = 0.02\,\text{m}^2$

4. About the given time (1 hour 30 minutes)

The time is not needed here because force depends on intensity and area:

$F = \frac{IA}{c}$

If intensity is constant, the average force is independent of the duration.

5. Check options

• A: $20\,\text{m}^2$ ❌
• B: $0.2\,\text{m}^2$ ❌
• C: $0.1\,\text{m}^2$ ❌
• D: $0.02\,\text{m}^2$ ✅

Therefore, the correct answer is D.