The power from the Sun is intercepted by
the cross-sectional area of the Earth pr^{2}.
Since C = 2pr then

Cross-section area= C^{2}/4p = (40000X10^{3})^{2}/4p
= 1.273X10^{14} m^{2} (This answer will be needed in question
2.)
Solar intensity = 1.35 kW/m^{2}

Total power = 1.273X10^{14} X 1.35 = 1.72X10^{14} kW

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