3. On the Earth, a mirror of area \( 1 \mathrm{~m}^{2} \) is held perpendicular to the Sun's rays.
(a) What is the force on the mirror due to photons from the Sun, assuming that the mirror is a perfect reflector? The momentum flux density from the Sun's photons is \( J_{\text {sun }}=4.6 \times 10^{-6} \mathrm{~kg} /\left(\mathrm{m} \cdot \mathrm{s}^{2}\right) \).
(b) Find how the force varies with angle if the mirror is tilted at angle \( \alpha \) from the perpendicular.
