A thermometer reading 65° F is placed in an oven preheated to a constant temperature. Through a glass window in the oven door, an observer records that the thermometer reads 110° F after 1 2 minute and 140° F after 1 minute. How hot is the oven?

Respuesta :

The temperature of the oven is 200°F

Explanation:

Given-

We have to apply Newton's law of cooling or heating

[tex]\frac{dT}{dt} = k ( T - Tm)\\\\\frac{dT}{T - Tm} = kdt[/tex]

On Integrating both sides, we get

[tex]T = Tm + Ce^k^t[/tex]

On putting the value,

T(0) = 65°F

[tex]65 = Tm + C\\C = 65 - Tm\\\\T = Tm + (65 - Tm) e^k^t[/tex]

After 1/2 minute, thermometer reads 110°F. So,

[tex]110 = Tm + (65 - Tm)e^0^.^5^k[/tex]                - 1

After 1 minute, thermometer reads 140°F. So,

[tex]140 = Tm + (65 - Tm)e^k[/tex]                     - 2

Dividing equation 2 by 1:

[tex]e^k^-^0^.^5^k = \frac{140 - Tm}{110 - Tm} \\\\e^0^.^5^k = \frac{140 - Tm}{110 - Tm}[/tex]                                - 3

From 1 we have,

[tex]e^0^.^5^k = \frac{110 - Tm}{65 - Tm}[/tex]

Putting this vale in eqn 3. We get,

[tex]\frac{110 - Tm}{65 - Tm} = \frac{140 - Tm}{110 - Tm}[/tex]

[tex](110-Tm)^2 = (140-Tm) (65-Tm)\\\\12100 + Tm^2 - 220Tm = 9100 - 140Tm - 65Tm + Tm^2\\\\3000 - 220Tm = -205Tm\\\\3000 = 15Tm\\\\Tm = 200[/tex]

Therefore, the temperature of the oven is 200°F

The Temperature ( hotness )  of the oven is ; 200°F

Given data :

Initial thermometer reading ( To ) = 65°F

Thermometer reading after 1/2 minute ( T1/2 ) = 110°F

Thermometer reading after 1 minute ( T1 ) = 140°F

Temperature of oven ( Tm ) = ?

Determine the Temperature  of the Oven

To determine the temperature of the oven we will apply Newton's law of heating and cooling.

[tex]\frac{dT}{dt} = K(T -Tm )[/tex]    (  Integrating the expression we will have )

T = Tm + [tex]Ce^{kt}[/tex]   ---- ( 1 )

where k = time

at T = 0 equation becomes

65 = Tm + C

∴ C = 65 - Tm

Back to equation ( 1 )

T = Tm + ( 65 -Tm )[tex]e^{kt}[/tex]  ---- ( 2 )

After 1/2 minute equation 2 becomes

110 = Tm + ( 65 - Tm )[tex]e^{0.5k}[/tex] ---- ( 3 )

After 1 minute equation 2 becomes

140 = Tm + ( 65 - Tm )[tex]e^{k}[/tex]  ---- ( 4 )

Next step : Divide equation 4 by equation 3

[tex]e^{0.5k} = \frac{140 - Tm}{110 - Tm}[/tex]  ----- ( 5 )

Also From equation 3

[tex]e^{0.5k} = \frac{110 - Tm}{65 - Tm}[/tex]  --- ( 6 )

Next step : Equating equations ( 5 ) and ( 6 )

( 110 - Tm )² = ( 140 - Tm )( 65 - Tm )

3000 - 220 Tm = -205Tm

∴ Tm = 3000 / 15 = 200°F

Hence we can conclude that the temperature ( hotness ) of the oven is 200°F.

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