Question

Dhoni wants to drink tea, when it is at 50°C. He ordered tea which arrives at a temperature of 80°C. Tea takes one minute to cool
from 80°C to 60°C. If room temperature is 30°C, how long he has to wait to drink the tea?​

Answer 1

Given :

T₁ = 80° C

T₂ = 60° C

T₃ = 50° C

Takes 1 min one minute to cool  from 80°C to 60°C.

Room temperature T₀ = 30° C

To find :

How long Dhoni has to wait to drink the tea?​

Solution :

$\frac{\delta t}{time}= k(\frac{T_1 + T_2}{2} -T_0)\\\\\frac{80-60}{60}=k(\frac{80+60}{2} - 30 )\\\\1 /3 =k(40)$

k = 1 / 120

$\frac{60-50}{time} =\frac{1}{120} (\frac{60+50}{2} - 30 )$

Time = 48 sec

Dhoni has to wait for 48 sec to drink the tea