Hello, 1. The problem statement, all variables and given/known data The volume of the container in the attachment is given as V. The container is filled with a fluid whose heat capacity is C and whose viscosity decreases linearly with the temperature. The fluid is initially at temperature T0, and a pipe carries fluid at temperature Tin into it and at a rate which is equal to the rate of the volume lost from the container (i.e. its dV/dt). I am asked to find the time at which the temperature in the container will be T. 2. Relevant equations 3. The attempt at a solution M/V = ρ m(t) = ρVt/τ0, where m(t) denotes the mass of water which passed through the pipe after time t. dQ/dt = [ρV/τ0]*Cw(T(t) - Tc) = ρVCwdT/dt Hence, dT/dt = (Tc - T(t))/T0 Hence, T(t) = Tc + (TH - Tc)e-t/τ0 = Tin + (T0 - Tin)e-t/τ0 t = -τ0ln((T - Tin)/(T0 - Tin)) Is that correct?