Question

Hot water cools from `60^@C` to `50^@C` in the first 10 min and to `42^@C` in the next 10 min. The temperature of the surrounding is
A. `5^@C`
B. `10^@C`
C. `15^@C`
D. `20^@C`

Answer 1

Correct Answer - B
`(theta_1-theta_2)/(t)prop[(theta_1+theta_2)/(2)-theta]`
for the first condition
`(60-50)/(10)prop[(60-50)/(2)-theta]implies1=K[55-theta]` .(i)
For the second condition
`(50-42)/(10)prop[(50+42)/(2)-theta]implies0.8=K(46-theta)` .(ii)
From Eqs. (i) and (ii), we get `theta=10^@C`