A solid aluminium ball, when quenched in a water bath maintained at 40°C, cools down from 550°C to 450°C in 20 seconds. The expected temperature of the ball after next 20 seconds may be about ____________________ °C?
Correct answer: A. 370
- A. 370
- B. 340
- C. 320
- D. 300
Explanation
Newton’s law of cooling makes the temperature excess above the bath temperature fall by the same ratio in equal time intervals. The first ratio is (450−40)/(550−40)=0.804, so the next temperature is about 40+0.804(410)=370°C.
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