A) 3.5
B) 14
C) 7
D) 10
E) 21
Correct Answer: C
Solution :
From Newtons law of cooling \[\frac{{{\theta }_{1}}-{{\theta }_{2}}}{t}=\left( \frac{{{\theta }_{1}}+{{\theta }_{2}}}{2}-{{\theta }_{0}} \right)\] Therefore, \[\frac{60{}^\circ -40{}^\circ }{7}\propto \left( \frac{60{}^\circ +40{}^\circ }{2}-10{}^\circ \right)\] ?. (1) \[\frac{40{}^\circ -28{}^\circ }{t}\propto \left( \frac{40{}^\circ +28{}^\circ }{2}-10{}^\circ \right)\] ?. (2) \[\therefore \] \[t=7\,s\]You need to login to perform this action.
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