Question

The temperature of a liquid drops from 365 K to 361 K in 2 min. Find the time during which the temperature of the liquid drops from 344 K to 342 K.

(Take, room temperature = 293 K)

Options

• 72 s

• 66 s

• 60 s

• 84 s

Answer 1

84 s

Explanation:

According to Newton's law of cooling,

`(T_1 - T_2)/2 = K((T_1 + T_2)/2 - T_0)`

`(365 - 361)/2 = K[(365 + 361)/2 - 293]`

⇒ K = `1/35`

Again, `(344 - 342)/t = 1/35[(344 + 342)/2 - 293] = 10/7`

t = `14/10` min = 84 s