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Jan16-13, 09:48 AM   #2
mfb
 
Mentor
1.assume i am riding a motorcycle at 100km/h, but i ride the motorcycle inside a very long train which is moving at also 100km/h. What speed do i have reported to the world? 200km/h?
If you ride in the same direction, measure ground speed and neglect special relativity, yes.

2.what happens at a short circuit? practically there is no resistance so the value of the current is infinity? therefore 3v battery can generate infinite curent if the wires have 0 resistance?
The battery has an internal resistance, which limits current. Without resistance and in a static (time-independent) setup, you cannot have a voltage.
3.is ot possible to have such a great resistance inside a circuit in order to stop a circuit from working? same as an open circuit?
An open circuit is just a huge resistance at some point.