You could hav emany scenarios...
1) you could have one app that is highly optimised that will you 100% of both cores...
2) you could have 2 single threaded appps that each peg one core fully...
3) you could have any combination of multiple apps adding up to use both cores....
Basic fact is you have 2 cpus under 1 hood..bottom line....whether you feed them the threads from one app or multiple app no single core will compete overall when you fully load them...