A man named Harold is standing in a train car that has no windows. Since there aren't any windows, he doesn't know how fast or in what direction the train is moving or whether it is accelerating or decelerating. Harold decides that he might be able to figure something out by dropping a tennis ball and watching where it lands. He does know which way the front of the train is, so when he does his ball-drop experiment he is facing forward. To make his experiment easier, Harold draws a red X on the floor of the train car. He then holds the tennis ball directly over the X, and releases the ball from a height of about five feet.
Harold tries his experiment he drops the ball, it lands behind the red X (in between his feet and the X).
What can Harold conclude about the train's velocity?
A The train is moving forward.
B The train is moving backward.
C The train isn't moving.
D He hasn't learned anything about the train's velocity.
What can Harold conclude about the train's acceleration?
A The train is undergoing forward acceleration.
B The train is undergoing backward acceleration.
C The acceleration is zero.
D He hasn't learned anything about the train's acceleration.
D
A
The train and the ball are moving at the same velocity when he drops the ball. Therefore unless the train accelerates the ball will go straight to the x. If it lands behind the x, the train is speeding up but the ball is not.