Here in the US most exams are an hour or an hour and a half long, depending on how long the class normally is. Final exams are usually three hours at most universities I think. However there are exceptions, for instance my first semester of E&M we had exams from 8pm-midnight on Mondays. *shudders*
Anyway, like e.bar.goum said, if you have a diagnosed learning disability you can get an exception from the school usually to have longer exam sessions. Otherwise, physics exams are not only to test your knowledge of the material, but your proficiency at doing the physics and math, so speed has to be taken into account.