A freezing system starts cooling the room at the rate of 4 degree Celsius per hour. If at the beginning, the temperature is30 degree Celsius, find the number of hours it takes to lower the room temperature to -2 degree Celsius ???

Solution:

Rate of cooling = 4^o Celcius/Hr.

Present temp. of the room = 30^o Celcius

Final temp. of the room = - 2^o Celcius.

So the drop in temp. = 30 - (-2) = 30 + 2 = 32^o.

To fall 4^o the time taken = 1 Hr.

To fall 32o the time taken will be = 1/4 x 32 = 8 Hrs.

Ans: 8 Hours.