Question

If \(t_1\) is the time taken for a body to cool from \(80^\circ\text{C}\) to \(75^\circ\text{C}\) and \(t_2\) is the time taken to cool from \(75^\circ\text{C}\) to \(70^\circ\text{C}\), then \[ t_1:t_2= \] \[ (\text{Temperature of surroundings}=30^\circ\text{C}) \]

• A. \(19:21\)
• B. \(17:19\)
• C. \(7:9\)
• D. \(9:11\)

Hint:

For Newton's law of cooling, \[ \boxed{ t\propto \ln\left(\frac{\theta_1}{\theta_2}\right), \qquad \theta=T-T_s. } \] Always use the excess temperature above the surroundings, not the actual temperature.

Answer 1

The Correct Option is B