Question

A student in the front of a school bus tosses a ball to another student in the back of the bus while the bus is moving forward at constant velocity. The speed of the ball as seen by a stationary observer in the street:

Could anyone explain why is the answer: "may be either greater, smaller, or equal to that observed inside the bus." ?

Answer 1

The bus is moving forward at a constant velocity. The ball, who threw the ball and who received the ball are inside the bus with a velocity equal to the velocity of bus. So the velocity of bus relative to the observer inside the bus is zero.

Now the observer inside the bus observed the ball from inside the bus, so he will just observed the ball is thrown from the front to back with velocity v relative to observer inside the bus.

Now the observer outside the bus observe the bus is moving forward with velocity u relative to his reference point, and also seen the ball is threw from front to back. But the velocity of the ball relative to observer outside the bus is velocity of the bus relative to observer outside the bus minus velocity of ball relative to observer inside the bus.

So, the velocity of the ball relative to observer outside the bus is = (u-v)