Part a
Using the power versus t plot for 0<=t<=10s calculate the energy delivered to the circuit element at t=1 s .
Part b
Calculate the energy delivered to the circuit element at t=6 s
part c
Calculate the energy delivered to the circuit element at t=10s .

can anyone help me??
thank you very much!!!

 

The question is firstly asking you to plot the instantaneous power function p(t)=i(t) x v(t). In other words plot i(t) [the top graph] multiplied by v(t) [the bottom graph] for t=0 to 10 seconds.

The energy W(tx) delivered at any time 'tx' is the summation of the area under the p(t) curve from t=0 to tx seconds. Having plotted the instantaneous power curve you should then be able to plot the energy curve by adding up the areas under p(t). This may involve some simple integration.

 

How do I multiple two graph? Sorry about I ask a stupid question

 

Look at the two graphs. Select several time values and multiply the i(t) and v(t) values at those times to give a p(t) value at that time. Plot those p(t) values against a time scale corresponding to the i(t) and v(t) time axes. Take some care when the v(t) function values switch instantaneously at certain times (1sec, 3sec, 5sec and 7sec). A clear picture should emerge after a few values are calculated.

At t=0 sec i(0)=0 and v(0)=5 so p(0)=i(0)*v(0)=0

At t=0.5 sec i(0.5)=10 and v(0.5)=5 so p(0.5)=i(0.5)*v(0.5)=50

At t=1 sec i(1)=20 and v(1)=(5) so p(1)=i(1)*v(1)=100

For t>1 sec but less than 3sec v(t) =0 so p(t) in that range is also zero.

And so it goes on.