Hi, I need help with the second part of this problem. I calculated the first par

Question

Hi, I need help with the second part of this problem. I calculated the first part to be 1.0296e5 W.

Here is the question:

The Sun delivers about 780 W/m2 of electromagnetic flux to the Earth’s surface.
Calculate the total power incident on a roof of dimensions 6 m × 22 m, assuming the radiation is incident normal to the roof.
Answer in units of W.

For this part I calculated: Area of the roof: 6 x 22 = 132 m2
Then: (780 W/m2 ) * (132 m2 ) = 1.0296e5 W

This is the part I am asking about:

Assume the roof is a perfect absorber. Determine the radiation pressure. Answer in units of Pa.

I divided: 1.0296e5 W / 3.0e8 m/s = 3.432e-4 N/m2 (but this answer is incorrect)

If I calculate it this way, am I not assuming the radiation is "partially reflected" and "partially absorbed" though?

Thanks in advance!

Explanation / Answer

The radiation pressure is(perfect absorption) P = I/c = (780 W/m2)/(3 x 10^8 m/s) = 2.6 x10^-6 Pa

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