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Dmitry [639]
3 years ago
12

Newton's law of cooling is , where is the temperature of an object, is in hours, is a constant ambient temperature, and is a pos

itive constant. Suppose a building loses heat in accordance with Newton's law of cooling. Suppose that the rate constant has the value Assume that the interior temperature is , when the heating system fails. If the external temperature is , how long will it take for the interior temperature to fall to

Physics
1 answer:
kirill [66]3 years ago
3 0

Complete Question

The complete question is shown on the first uploaded image

Answer:

The time taken  is  t  = 6.89 \ hrs

 

Explanation:

From the question we are told that

       The value of  k = 0.15hr^{-1}

       The  the interior temperature is  u(t = 0) =  70 ^oF

         The external temperature is  T  = 11 ^oF

          The required interior temperature is  u_{t} = 32 ^oF

      The newton cooling law is

                      \frac{du}{dt}  =  -k (u -T)

=>                 \frac{du}{u-T}  = - kdt

  Now integrate both sides we have  

                 \int\limits \frac{du}{u-T}  =\int\limits   - kdt

                   ln (u - T) =  -kt + c    

Since c is a constant lnC = c   will also give a constant so

                 ln (u - T) =  -kt + ln C    

       =>       \frac{(u -T)}{C}  =  e^{-kt}

     =>        u = T + Ce^{-kt}  

          substituting value

                  70 = 11 +Ce^{-0* 0.15}

                  C = 59

Hence

        u_t =  11 + 59 e^{-0.15 *t}

       32=  11 + 59 e^{-0.15 *t}

=>     t  =  -\frac{ln(\frac{21}{59} )}{0.15}

         t  = 6.89 \ hrs

 

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