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Mechanical Properties Of Fluids

Question
CBSEENPH11019828

Find the time in which a layer of ice 3cm thick on the surface of pond will increase by 2mm when the temperature of air is –25°C. Take density of ice 900kg/m3and thermal conductivity 0.005cal/msK.

Solution

Initial thickness of layer of ice, x1 = 3 cm 
Final thickness of ice, x2 = 3.2 cm
Temperature of air, straight theta= -25o
Density of ice, straight rho= 900 kg/m
Thermal conductivity, K = 0.005 cal/msK 
Time taken to freeze the lake from thickness to x1 is given by, 
straight t space equals space fraction numerator ρL over denominator 2 Kθ end fraction left parenthesis straight x subscript 2 squared space minus space straight x subscript 1 squared right parenthesis thin space

straight t space equals space fraction numerator 0.9 cross times 80 over denominator 2 cross times 0.005 cross times 25 end fraction open square brackets left parenthesis 3.2 right parenthesis squared minus left parenthesis 3 right parenthesis squared close square brackets space

space space equals fraction numerator 90 cross times 80 over denominator 25 end fraction open square brackets left parenthesis 3.2 right parenthesis squared minus left parenthesis 3 right parenthesis squared close square brackets space

space space space equals space 357.12 space straight s