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Earth receives 1400   W   m - 2 of solar power. If all the solar energy falling on a lens of area 0 . 2   m - 2 is focussed on to a block of ice of mass 280   g , then what is the time (in min ) taken by the ice to melt completely? [ L fusion = 3 . 3 x 105   J   kg - 1 ]

Correct answer

5.5

Step-by-step solution

Heat required to melt the block = (0.28kg) (3.3 x 10 5 J/kg)= 9. 24 x 10 4 J Heat received per second = (1400J/ m 2 ) (0. 2m 2 ) = 280 J Time taken (in minutes) = 9.24 × 1 0 4 280 × 60 = 5. 5

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