Unit: motion in a plane
Year: 1994 Question#: 63
Question: During the flight of the ball, what is the direction of its acceleration?
(1 ) downward
(2 ) upward
(3 ) westward
(4 ) eastward
What is this question really asking?
Explanation by: Abby R.
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Answer 1
downward
CORRECT
The acceleration of the ball is downward because the force accelerating the ball is gravity. As we all know from normal everyday experience, gravity pulls us downward. Now, when looking at this question, you can figure out that the only acceleration of the ball is gue to gravity, because no other force is being applied. The ball starts with a constant horizontal velocity, so it is not accelerating horizontally. The only thing "pulling" on the ball is gravity. Just by looking at the diagram, you can tell that it is accelerating downward because its path is curving downward.
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Answer 2
upward
INCORRECT
The ball is not accelerating upward because gravity, the only force accelerating the ball, pulls downward. If the ball were accelerating upward, it's path would curve upward, in the direction of the acceleration. But it doesn't; it curves downward. So upward is not the answer.
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Answer 3
westward
INCORRECT
As I have said before, the ball's only acceleration is downward., the acceleration of gravity. The ball could not be accelerating westward because then it's horizontal velocity would be decreasing. In the diagram, it is given that the horizontal velocity is constant, 20 m/s east. return to top
Answer 4
eastward
INCORRECT
The only acceleration the ball experiences is downward, the acceleration of gravity. So the acceleration couldn't be eastward. But you can also tell that it's not eastward because otherwise the horizontal velocity would be increasing, and it's given to be 20 m/s east. Finally, you can tell the acceleration is not eastward because the path is curving downward. Therefore, the acceleration must be downward. A horizontal acceleration would not cause the path to change at all, because it is in the same dimension as the velocity. return to top
What's this question really asking?
This question is asking you two things: What acceleration is acting on the ball, and in what direction is that acceleration? Even if you don't know why the ball is accelerating downward, you should be able to tell, by looking at the ball and the curvature of its path, in what direction it is accelerating.
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