The only possibility of the heat flow in a thermos flask is through its cork which is \( 75 \mat...
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0The only possibility of the heat flow in a thermos flask is through its cork which is \( 75 \mathrm{~cm}^{2} \) in area and \( 5 \mathrm{~cm} \) thick (see figure). Its thermal conductivity is \( 0.00075 \mathrm{cal} / \mathrm{cm} \mathrm{s}^{\circ} \mathrm{C} \). the outside temperature is \( 40^{\circ} \mathrm{C} \) and latent heat of ice is \( 80 \mathrm{cal} / \mathrm{g} \). Time taken by \( 500 \mathrm{~g} \) of ice at \( 0^{\circ} \mathrm{C} \) in the flask to melt into water at \( 0^{\circ} \mathrm{C} \) is
(A) \( 2.47 \mathrm{~h} \)
(B) \( 4.27 \mathrm{~h} \)
(C) \( 7.42 \mathrm{~h} \)
(D) \( 4.72 \mathrm{~h} \)
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