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# Newton's law of cooling states that the temperature of an object decreases as a function of time?

according to T=Ts+(T0-Ts)e^-kt, where T 0 is the initial temperature of the liquid, Ts is the surrounding temperature, and k is a constant. For a time in minutes, the constant for coffee is approximately 0.283. The corner coffee shop has an air temperature of 70 F and serves coffee at 206 F. Coffee experts say coffee tastes best at 140 F.

a. How long does it take for the coffee to reach it's best temperature?

b. The air temperature on the patio is 86 F. How long does it take for coffee to reach it's best temperature there?

### 3 Answers

- RogueLv 78 years agoFavorite Answer
a) 140 = 70 + (206 - 70)e^(-0.283t)

=> 140 = 70 + 136e^(-0.283t)

=> 70 = 136e^(-0.283t)

=> 70/136 = e^(-0.283t)

=> ln(35/68) = -0.283t

=> t = -ln(35/68)/0.283

=> t = 2min 20.8 sec (1 dp)

b) 140 = 86 + (206 - 86)e^(-0.283t)

=> 54 = 120e^(-0.283t)

=> ln(9/20) = -0.283t

=> t = -ln(9/20)/0.283

=> t = 2 min 49.3 sec (1 dp)

- bhamaraniyamaLv 45 years ago
I'm assuming your M is the outside temperature, so on this case, this is resolve (a) 1) Distribute within the ok dT/dt = kM - kT 2) move the kT to the opposite side dT/dt + kT = kM 3) Use an integrating component: intg is the fundamental µ = e^(intg(okay)dt) µ = e^kt four) Multiply it during and clear up for the rest of the necessary! E^kt*dT/dt + e^kt*kT = e^kt*kM combine: e^kt*T = intg(kM*e^kt)dt e^kt*T = M*e^kt + C 5) remedy for T T = M + C(e^-kt) M = outside Temperature C = steady ok = price of exchange To clear up for (b), it can be with no trouble plug within the values and solve for the respecting k and C. T = M + C(e^-kt) So by way of stating that the thermometer reads 100 degrees firstly, that implies T(zero) = one hundred through after 6 minutes, temperature is eighty, so: T(6) = 80 The medium can also be 70 degrees, indicating the initial temperature. Plug some values in and experiment it out. One hundred = 70 + C if t = 0, then e^-kt = 1 consequently C is 30. By way of then utilising the T(6) = 80, that you can resolve the okay. 80 = 70 + 30(e^-k(6)) clear up for k now. 10 = 30(e^-6k) 1/three = e^-6k ln(1/three) = -6k -ln(1/3)/6 = k consequently, k =~ 0.18 So the ultimate equation is: T = 70 + 30(e^-0.18t) Plug in 20 for t and resolve for T afterwards, T = 70.8º Which is logical as the temperature will ultimately reach the temperature of the median at 70º.

- Mike GLv 78 years ago
a) T=Ts+(T0-Ts)e^-kt

140-70 = 136e^(-0.283t)

ln(70/136) = -0.283t

t = 2.35 minutes

b) 140-86 = 120e^(-0.283t)

ln(54/120) = -0.283t

t = 2.82 minutes