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Solution


Q.

A body cools from 80°C to 60°C in 5 minutes. The temperature of the surrounding is 20°C. The time it takes to cool from 60°C to 40°C is            [2023]
1 500 s  
2 253 s  
3 450 s  
4 420 s  

Ans.

(1)

Rate of cooling ∝ Temperature difference

80-605=k{70-20}                         ...(i)

60-40t=k{50-20}                        ...(ii)

4t20=5030

t=253 min=500 sec

⇒ t=500 sec