Suppose a person riding on top of a freight car shines a searchlight beam in the direction in which the train is traveling. Compare the speed of the light beam relative to the ground when:
a. The train is at rest.
b. The train is moving.

How does the behavior of the light beam differ from the behavior of a bullet fired in the same direction from the top of the freight car?

Explanation:

a ) The speed of light will be 3 x 10⁸ m /s

b ) Speed of light will again be  3 x 10⁸ m /s . for an observer on the ground. It is so because speed of light is independent of moving frame of reference . It is absolute . It can not be changed by changing frame of reference .

The behavior of light differs because the speed of bullet will be less in case of stationary train . For moving train , speed of bullet will be increased by amount equal to speed of train for an observer on the ground.