A) \[25{}^\circ C\]
B) \[30{}^\circ C\]
C) \[35{}^\circ C\]
D) \[45{}^\circ C\]
Correct Answer: B
Solution :
According to Newtons law of cooling, \[\frac{{{\theta }_{1}}-{{\theta }_{2}}}{t}=\alpha \left[ \frac{{{\theta }_{1}}+{{\theta }_{2}}}{2}-{{\theta }_{0}} \right]\] For the given conditions \[\frac{70-50}{5}=\alpha \left[ \frac{70+50}{2}-20 \right]\] ?(i) Let \[\theta \] be the temperature after next 10 min. Then, \[\frac{50-\theta }{10}=\alpha \left[ \frac{50+\theta }{2}-20 \right]\] ?(ii) Solving Eqs. (i) and (ii), we get\[\theta =30{{\,}^{o}}C\]
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