Answer to Question #211165 in Physics for Ena

Question

A woman stands on top of a moving railroad car and tosses a ball straight up in the air. If there is no air resistance, where will the ball come back down? Explain your answers

Answer 1

When the ball is in the air, it takes part in the two movements: vertical and horizontal ones. There are two possible cases:

1) The car is moving with the constant speed.

2) The car is moving with the variable speed.

Let's consider the first case. In this case when the ball leaves the car its horizontal speed is equal to the speed of the car. Since there is no air resistance (and thus no force that can slow the ball), then, according to the first Newton's law, the speeds of the car and the ball remain the same. Thus, the ball will come back down at the same spot (relatively to the car) from which it was launched.

In the second case, the horizontal speed of the ball is equal to the instantaneous speed of the car at the moment of the launching. Again, according to the first Newton's law the ball does not change its horizontal speed during the motion. But now the car changes its speed. Thus, the ball will come back down ahead or behind the car, depending on the direction of car's acceleration.