To help prevent frost damage, fruit growers sometimes protecttheir crop by spray

Question

To help prevent frost damage, fruit growers sometimes protecttheir crop by spraying it with water when overnight temperaturesare expected to go below the freezing mark. When the water turns toice during the night, heat is released into the plants, therebygiving them a measure of protection against the fallingtemperature. Suppose a grower sprays 8.76 kg of water at 0°Conto a fruit tree. (a) How much heat is releasedby the water when it freezes? (b) How much wouldthe temperature of a 191-kg tree rise if it absorbed the heatreleased in part (a)? Assume that the specific heat capacity of thetree is 2.5 x 103 J/(kg C°) and that no phase changeoccurs within the tree itself.

Explanation / Answer

a) EL=mL EL=(8.76 kg)(334 kJ/kg)(1000 J/kJ) EL= 2.93 x 106 J b) 2.93 x 106 J = (191 kg)(2.5 x 103 J/kg C)(T) T = 6.12 C

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