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No. They were quite expensive back in the days.
They can be, but due to the cost, it's quite rare.
Because you are braking hard and possibly have low quality pads. -Beware, many cheap pads out there now. If you want them to last buy well known name brand. Most parts stores will give 3 prices for pads -never pick the lowest !
There is no "best" material. They all have different characteristics, so what's "best" is determined by which features you prefer the most. Some will last longer, but brake poorer. Others will brake better, but wear out faster. Some are good in rain but might fail in the dry. Kool stop "Salmon" (b/c of the color) are quite popular.
probably, if the pads are worn, or the rotors \ drums are scarred, there will be a grinding noise, plus you should be able to feel it through the brake pedal. most modern brake systems have quealers on the pads to tell you when they are getting worn and should be replaced. If you have a disc brake system, you should be able to inspect the rotors quite easily. Look for gouges in the surface of the rotor. If they are badly gouged, they should be turned or replaced.
You will need to remove the road wheel and then the bolts holding the brake caliper. The brake rotor can then be removed. Quite a simple job but you should take digitial pics of the brake pads and shim location position as it is easy to get these wrong when re-assembling. Suggest replacing the rotor and brake pads at the same time. I replaced the plain rotors with drilled / grooved ones to improve wet weather brake performance.
No. there are quite a few other places where you can add an electric motor to a bicycle. However, the hub motor is quite probably the one which requires the least amount of changes to the rest of the bike.
That is strictly a function of your driving style and the type of driving. Brake pads can wear as fast as ten thousand miles or last even longer than one hundred thousand miles, depending on how often and how hard the brake pedal is pressed. If the brakes are used so often that they overheat, or if the driver "rides" the brake pedal, the rotors will warp, resulting in a pulsing sensation when you use moderate braking. In any case, brakes are generally quite durable, but drivers are quite unpredictable.
Since they were carved from a piece of stone I would imagine a few weeks. They only had bronze tools at the time and they need to be replaced quite often.
No. It is quite dangerous but first he/she needs to know how to ride the bicycle and/or the car.
Oh sure. Carbon fiber frames are composites, and quite popular.
Quite simply...NO!