WindowlessTrainCar.problem A man named Harold is standing in a train car that ha
ID: 1594915 • Letter: W
Question
WindowlessTrainCar.problem
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.
The first time he drops the ball, it lands directly below his release point, right on the red X.
1)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.
2)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.
A little while later, Harold tries his experiment again. This time, when he drops the ball, it lands behind the red X (in between his feet and the X).
3)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.
4)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.
Harold is bored, because there really isn't anything to do when locked in a windowless train car. So he decides to entertain himself by doing the ball drop experiment one last time. This time, the ball lands in front of the red X (farther away from him than the red X).
5)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.
6)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.
Explanation / Answer
1)
a)The train is moving forward.
The train is moving forward with a constant velocity. The net horizontal force is zero and it lands on the same spot.
2)
c)The acceleration is zero.
Since the train is moving with a constant velocity, the acceleration is zero. As the train is not accelerating the inertia of bodies remains same.
3)
a)The train is moving forward.
If the tarin is moving backwards then the ball must have landed before the X spot.
4)
a)The train is undergoing forward acceleration.
The train got forward acceleration that is why this time the ball did not land on the X spot. The inertia of the body gets altered and there would be a net horizontal force acting on the ball leading to its land at a different point.
5)
b)The train is moving backward.
6)
b)The train is undergoing a backward acceleration.
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