Question

Certain quantity of water cools from 70$^{\circ}$C to 60$^{\circ}$C in the first 5 minutes and to 54$^{\circ}$C in the next 5 minutes. The temperature of the surroundings is

• A. $ 45 ^\circ C $
• B. $ 20 ^\circ C $
• C. $ 42^ \circ C $
• D. $ 10 ^\circ C $

Answer 1

Answer: (A)

$\frac{60-70}{5}=- K (65- T )$
$\frac{54-60}{5}- K (57- T )$
$\frac{-10}{-6}=\frac{65- T }{57- T }$
$285-5 T =195-3 T$
$90=2 T$
$T =45^{\circ}$