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A cup of tea cools from 65*5^(@)C in one minute in a room of 22*5^(@)C. How long will the same cup of tea to cool from 46*5^(@)C to 40*5^(@)C in the same room. (Choose the nearest value in min.) : |
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Answer» 1 `(theta_(1)-theta_(2))/(t)=k[(theta_(1)+theta_(2))/(2)-theta_(0)]` where `theta_(0)` is temp. of surroundings. `:.""(65*5-32*5)/(1)=k[(65*5+62*2)/(2)-22*5]`. . . (i) Also `(46*5-40*5)/(t)=k[(46*5+40*5)/(2)-22*5]`. . . (ii) DIVIDING (i) by (ii) `t/2=(64-22*5)/(43*5-22*5)` `rArrt=4` min. Correct CHOICE is (d). |
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