Problem 22.2 A closed system undergoes a process during which there is heat transfer to the system at a constant rate of 5 kW, and the power out of the system varies with time according to Wout = {+2.5t (+2.5t 0 2.0 h where t is in hours and Wout is in kW. (a) Sketch the system and label the energy flows. (b) Determine the time rate of change of system energy at t = 1.2 h and 2.4 h, in kW (c) Determine the change in system energy after 3 h, in kW.h and in kJ. Ans: b) 1.8 kW ≤ dE/dt@1.2 h ≤ 2.2 kW c) 5 kW.h ≤AE ≤ 6 kW.h

Problem 22.2 A closed system undergoes a process during which there is heat transfer to the system at a constant rate of 5 kW, and the power out of the system varies with time according to Wout = {+2.5t (+2.5t 0 2.0 h where t is in hours and Wout is in kW. (a) Sketch the system and label the energy flows. (b) Determine the time rate of change of system energy at t = 1.2 h and 2.4 h, in kW (c) Determine the change in system energy after 3 h, in kW.h and in kJ. Ans: b) 1.8 kW ≤ dE/dt@1.2 h ≤ 2.2 kW c) 5 kW.h ≤AE ≤ 6 kW.h

Elements Of Electromagnetics

7th Edition

ISBN:9780190698614

Author:Sadiku, Matthew N. O.

Publisher:Sadiku, Matthew N. O.

ChapterMA: Math Assessment

Section: Chapter Questions

Problem 1.1MA

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Question

Problem 22.2
A closed system undergoes a process during which there is heat transfer to the system at a constant rate of 5 kW,
and the power out of the system varies with time according to
(+2.5t
+5.0
Wout={+2
0<t≤ 2.0 h
t> 2.0 h
where t is in hours and Wout is in kW.
(a) Sketch the system and label the energy flows.
(b) Determine the time rate of change of system energy at t = 1.2 h and 2.4 h, in kW
(c) Determine the change in system energy after 3 h, in kW.h and in kJ.
Ans: b) 1.8 kW ≤ dE/dt@1.2 h ≤ 2.2 kW
c) 5 kW.h ≤AE ≤ 6 kW.h

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