Grade 12 Physics: Relativity

During which period did physicists experience a sense of satisfaction with their understanding of the universe, before realizing a need for a new theory?

A person in a windowless railway car at constant velocity tosses a ball horizontally. What test can they perform to determine if the car is moving or stationary?

Charles moves in a high-speed train relative to Priya, who is at rest. Both measure time using a light clock. According to Priya, whose time moves slower?