Heat Generation Question
If you're given that 5 W is being dissipated by a component, than that strongly implies that it will be burning that as heat.  Other components around it will likely also be dissipating some heat as well, but you make it sound like this is some idealized academic question for you learning some thermal sim (FEA?) package.

For the parts that I've mostly dealt with&mdash;discrete MOSFETs&mdash;the "power rating" is usually given as a current rating under some conditions (easily convertible into watts), and it varies wildly depending on the thermal resistance from the junction (TJ, all that really matters) to ambient (TA).  A free standing part with no heat sinking may have several or dozens of times the thermal resistance compared with even modest heatsinks.  Additionally, the figure might be quoted at TA = 25 °C, not the actual maximum temperature your system will operate at, so even if you have a part that can dissipate 5 W, there might be some caveats.