1) if I take a very hot shower, do i sweat?
2) would a muscular person be less likely to gain weight because his/her body needs more food to maintain itself? (assuming same food intake)
3) when is it the best time to recharge my cell phone? empty battery? half empty? as often as I can?
4) in which situation do I have more chances to survive? a plane crash? or a helicopter crash? (at helicopter altitude)
5) does more expensive gasoline give me better gas mileage? and if so, does it make up for the extra cost?

1. yes
2. yes
3. half empty, it contains lithium batteries which don't have a "memory", like previous batteries.
4. plane, it can glide better
5. no, it prevents something called knocking, but it contains no more energy.

I concur with the goat.

1, Not just a hot shower, but you can sweat while swimming hard, but of course, you just don't notice.

2, Yes, muscle is active tissue, and therefore requires energy. So at equal weights, a muscular person needs more calories to maintain bodyweight than a fat person. Ironic, but these things tend to spiral, so but it shows that once on the right side of the body fat index, life gets a whole lot easier, so it's worth getting there.

3, Half empty is good, depends on how you use you phone. As stated, without memory problems, batteries can be recharged whenever, full depletion is no longer a best practice.

4, Plane. Statistically, flying in planes is still the safest form of transport.

5, Not any more, the star rating used to relate to Octane content, and more Octane meant better preformance. Now we all slosh the same old unleaded into out tanks, the only differences are a few additives to keep the engine clean.

5) does more expensive gasoline give me better gas mileage? and if so, does it make up for the extra cost?

If your vehicle requires a high octane then you must use it. It would be better to find a vehicle that uses low octane because it gives you the same power for allot less money. The higher compression an engine has will give it more power but must use a high octane fuel in order to work properly. :)