Question

Bottom of a lake is at $0^{\circ} C$ and atmospheric temperature is $-20^{\circ} C$. If $1 cm$ ice is formed on the surface in $24\, h$, then time taken to form next $1\, cm$ of ice is

• A. 24 h
• B. 72 h
• C. 48 h
• D. 96 h

Answer 1

Answer: (B)

Time intervals to change thickness from 0 to $x$ from $x$ to $2 x$ are in ratio of $1: 3: 5: 7 \ldots \ldots$
$\therefore t_{1}: t_{2}=1: 3$
$=24: 24 \times 3$
$\Rightarrow t_{2}=72$ hours