Energy balance: solar power input determines water temperature rise

Steps:

• Total power = panel area × output per m² = 30 m² × 300 W/m² = 9,000 W
• Time in seconds = 8 hours × 3,600 s/hour = 28,800 s
• Total energy Q = power × time = 9,000 W × 28,800 s = 259,200,000 J
• Temperature rise ΔT = Q / (mass × specific heat capacity) = 259,200,000 J / (500 kg × 4,200 J/kg °C) = 41 °C

Why D is correct:

• It follows the heat transfer formula Q = m c ΔT, where all input energy raises temperature with no losses.

Why the others are wrong:

• A: Results from dividing by extra factors like 3600 twice, underestimating energy.
• B: Assumes total output of 300 W instead of 9,000 W, ignoring area multiplication.
• C: Arises from approximate miscalculation of time conversion (e.g., using 3,000 s/hour).

Final answer: D