Aplate is removed from an oven at temperature of 50◦ and placed in a large room at 20◦ . after 5 minutes the temperature of the plate is 40◦ . how much longer will it take to reach 30◦ ?

Explanation:

The given data  is as follows.

Initial temperature () =

Room temperature () =

Time (t) = 5 min

Final temperature (T) =

According to the unsteady state equation,

where,       h = heat transfer coefficient

                  A = area

                 d = density

                 V = volume

                 C = specific heat capacity

All of these are constants and can be expressed as K

Therefore,          K =

                                                                                                          0.4055 = 5K  

                                        K = 0.0811

After 5 minutes, the new temperature will be as follows.  

         New temperature () =

                                   Time (t) = ?

Again, from the unsteady state conduction,

    =      

                                   1.0986 =

                                         t = 13.55 min

Thus, we can conclude that after 13.55 minutes the temperature reaches to .

i'm pretty sure its b i might be wrong though!