Properties Of Solids And Liquids Question 453

Question: A body cools from $ 50.0{}^\circ C $ to $ 49.9{}^\circ C $ in 5s. How long will it take to cool from $ 40.0{}^\circ C $ to$ 39.9{}^\circ C $ ? Assume the temperature of surroundings to be $ 30.0{}^\circ C $ and Newton’s law of cooling to be valid

Options:

A) 2.5 s

B) 10 s

C) 20 s

D) 5 s

Show Answer

Answer:

Correct Answer: B

Solution:

[b] $ \frac{50-49.9}{t}=K( \frac{50+49.9}{2}-30 ) $ ….(i)

$ \frac{40-39.9}{t}=K[ \frac{40+39.9}{2}-30 ] $ -(ii)

From equations (i) and (ii), we get$ t\approx 10 s $ .



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