A body cools from 80^(@)C to 50^(@)C in 5 minutes Calculate the time it takes to cool from 60^(@)C to 30^(@)C. The temperature of the surroundings is 20^(@)C.

A body cools from 80^(@)C to 50^(@)C in 5 minutes Calculate the time i

1.	A body cools from 80^(@)C to 50^(@)C in 5 minutes Calculate the time it takes to cool from 60^(@)C to 30^(@)C. The temperature of the surroundings is 20^(@)C.
Answer» Solution :According to Newton.s law of COOLING, `-(dT)/(dt)=K.(T-T_(s))` `-((50-80)/(5))=K.[(50+80)/(2)-20]` `6=K.(65-20)` `:.K.=(6)/(45)` Now, again, `-(dT)/(dt)=K.(T-T_(s))` `:.((30-60)/(t) )=(6)/(45)[(30+60)/(2)-20]` `:.(30)/(t)=(2)/(15)[45-20]` `:.(30)/(t)=(2)/(15)xx25` `:.(30)/(t)=(10)/(3)` `:.t=(90)/(10)` `:.t=9" min"`