1. Use Newton’s law of cooling

For a body cooling in surroundings of constant temperature $T_s$, the excess temperature decays exponentially:

$T - T_s = (T_0 - T_s)e^{-kt}$

where:

• $T$ = temperature of body at time $t$
• $T_s = 10^\circ \mathrm{C}$
• $k$ = cooling constant

2. Apply given data for first 7 minutes

Initially,

$T_0 = 60^\circ \mathrm{C}$

After 7 minutes,

$T = 40^\circ \mathrm{C}$

So the excess temperatures above surroundings are:

$60-10=50$ $40-10=30$

Hence,

$30 = 50e^{-7k}$

Thus,

$e^{-7k} = \frac{30}{50} = \frac{3}{5}$

3. Find temperature after next 7 minutes

After another 7 minutes, total time becomes 14 minutes. Again, the excess temperature gets multiplied by the same factor $\frac{3}{5}$ in each 7-minute interval.

At $t=7$ min, excess temperature is:

$40-10 = 30$

After next 7 minutes,

$\text{new excess temperature} = 30\cdot \frac{3}{5} = 18$

Therefore, the new temperature is:

$T = 10 + 18 = 28^\circ \mathrm{C}$

4. Check options

• A: $34^\circ \mathrm{C}$
• B: $28^\circ \mathrm{C}$ ✅
• C: $32^\circ \mathrm{C}$
• D: $30^\circ \mathrm{C}$

So the correct option is B.