[Ohm's law] Why does the answer key use the time after 5 seconds?

[bluesteels]

Homework Statement

A 10 Ω resistor carries a current that varies as a function of time as
shown. How much energy has been dissipated by the resistor after 5 s?

Relevant Equations

E= I^2 R delta t

This the answer key::

im confused because it say "how much energy has been dissipated after 5s". So shouldn't you be looking at the ground after 5 sec.

but apparently the solution look at it before 5 sec, am I missing anything, can someone explain

 

[Drakkith]

Yes, "after 5 seconds" means that 5 seconds has passed. Think of it as asking, "after 5 seconds has passed". We just get lazy and don't add the "has passed" part.

 

[bluesteels]

Yes, "after 5 seconds" means that 5 seconds has passed. Think of it as asking, "after 5 seconds has passed". We just get lazy and don't add the "has passed" part.

but on the answer key they got 3 sec before 5 second has passed. Do you see what I mean. The first pic is the question 2nd is the answer key.I'm confused on why are getting the value (3s) within 5 second interval when the question ask for after 5 second

 

[Orodruin]

In the 5 second interval, the current is only non-zero during 3 of those and when it is non-zero it is 2 A.

 

[Drakkith]

but on the answer key they got 3 sec before 5 second has passed.

For how many seconds out of those 5 is there current flowing through the resistor?

 

[Herman Trivilino]

I'm confused on why are getting the value (3s) within 5 second interval when the question ask for after 5 second

So, you are confused by the solution, not by the question? But you are also confused by the question, which prompted you to look at the solution. Try to understand the question and come up with a solution before you look at the solution. Otherwise, you will not be prepared for test questions and won't do well in the course.

The solution states clearly that during the first 5 seconds the current is 2 A for only 3 of those 5 seconds. Can you verify this by looking at the graph, or is it just something you assume must be true because it's stated in the solution?