Electrical Engineering - Energy Graph Question

[Larrytsai]

Homework Statement

Question number 3!, I attached it. Need help!

Figure 1 shows the current through and the voltage across a device. Find the total energy absorbed by the device fore the period 0<t<4.

Homework Equations

integral of p = energy
P=VI

The Attempt at a Solution

Just need the algorithm to solving these kinds of problems, I am kind of thrown off at the instantaneous change.

 

[mplayer]

One way you could think about this problem is by taking discrete intervals on the current graph and voltage graph and multiplying these values together. This will result in a graph that describes the power dissipation in the device over the given time interval. Then it will just be a matter of finding the area under the curve (integrating the resulting power function).

 

[Larrytsai]

Yeah I thought about that approach but when I look at the voltage it comepletely throws me off. I am able to break the current into 2 separate intervals with the function y1=25x and 0<t<2, y2=-25x 2<t<4, but for the voltage at t=2 its constant and I can't come up with a function to multply with my current.

 

[mplayer]

For the voltage between t=1 and t=3, the function describing the voltage is just a constant, or y=10.