Ice starts forming in a lake where the water is at `0^(@)C` and the ambient temperature is `-10^(@)C`. If the time taken for 1 cm of ice to be formed is 7 hours, then the time taken for the thickness of ice to change from 1 cm to 2 cm is

Options

A. `7` hours
B. `14` hours
C. less than `7` hours
D. more than `7` hours

Answer

D

Explanation

`because t prop(x_(2)^(2) - x_(1)^(2))`
For `x_(1) = 0 , X_(2) = 1`cm
` 7 prop (1^(2)-0^(2))`
For `x_(1) = 1` cm , `x_(2) = 2` cm
`t prop(2^(2) - 1^(2)) implies (7)/(t) = (1)/(3) implies t = 21` hrs