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johnsonc007

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**1. The problem at hand: A gas is contained in a closed rigid tank. An electric resistor in the tank transfers energy to the gas at a constant rate of 1000W. Heat transfer between the gas and the surroundings occurs at a rate of Q(dot) = -50t, where Q (dot) is in watts, and t is in time, minutes.**

(a) Plot the time rate of change of energy of the gas for 0<t<20 min in watts. (actually t is greater than or equal to 0, and t is less than or equal to 20)

(b) Determine the net change in energy of the gas after 20 minutes, in kJ

(a) Plot the time rate of change of energy of the gas for 0<t<20 min in watts. (actually t is greater than or equal to 0, and t is less than or equal to 20)

(b) Determine the net change in energy of the gas after 20 minutes, in kJ

2. I am not following on how to complete this task. I am confused by the Q(dot) equation. How can it equal watts when multiplied by minutes, as a watt is a J/s? Would get Q(dot)=Jmin/s....

3. I have tried to solve this numerous times, all with the wrong solution. I tried starting part b first as I need that data to do part a. I know that dE/dt = Q(dot) - W(dot). I drew two closed systems, one with the gas isolated with the resistor work entering and Q=0, and then another with the resister in the system and Q leaving the system, so that W=0. Am I on the right path? If so, what can I do with that? I found W=1200kJ but Q being some huge number and not working towards the correct solution.

Also took derivatives, but that got me nowhere fast too :(