The atmospheric temperature in the surroundings of a lake is -10 °C while the water in the lake is at 0 °C. If it takes 7 h to form 1 cm thick ice, then how much time is required to form another 1 cm of ice ?

Options

A. 7h
B. 14h
C. Less than 7h
D. More than 7h

Answer

D

Explanation

Time taken depends on thickness as, `t prop (x_(2)^(2) - x_(1)^(2))` where `t, x_(2)` and `x_(1)` are time, final thickness and initial thickness respectively.
Hence,
`7/t = (1^(2)-0^(2))/(2^(2)-1^(2))` where t is time taken in second case
On solving, we get t = 21 hours which is more than 7 hours.