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course Phy 121
1:15 pm July 6
A child in a slowly moving car tosses a ball upward. It rises to a point below the roof of the car and falls back down, at which point the child catches it. During this time the car neither speeds up nor slows down, and does not change direction.What force(s) act on the ball between the instant of its release and the instant at which it is caught? You can ignore air resistance.
answer/question/discussion:
The force of gravity and the muscular force of throwing the object
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What happens to the speed of the ball between release and catch? Describe in some detail; a graph of speed vs. clock time would also be appropriate.
answer/question/discussion:
The highest speed should be when the ball leaves the had and returns, the lowest speed should be when it reaches the top when it is thrown and stays still for a very short time, graph would be v shaped, speed would start out high, get lower and than get higher again
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Describe the path of the ball as it would be observed by someone standing along the side of the road.
answer/question/discussion:
Someone standing if the car was moving would see it about like the graph would look.
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How would the path differ if the child was coasting along on a bicycle? What if the kid didn't bother to catch the ball? (You know nothing about what happens after the ball makes contact with the ground, so there's no point in addressing anything that might happen after that point).
answer/question/discussion:
I would be really similar to riding in the car because it is in motion. If it was dropped though it would differ the graph and the downward motion would be faster.
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What if the child drops the ball from the (inside) roof of the car to the floor? For the interval between roof and floor, how will the speed of the ball change? What will be the acceleration of the ball? (You know nothing about what happens after the ball makes contact with the floor, so there's no point in addressing anything that might happen after that point).
answer/question/discussion:
The final velocity would have the highest speed and acceleration would be 9.8 m/s^2 (no other forces would be acting on it)
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What if the child holds the ball out of an open window and drops it. If the ball is dense (e.g., a steel ball) and the car isn't moving very fast, air resistance will have little effect. Describe the motion of the ball as seen by the child. Describe the motion of the ball as seen by an observer by the side of the road. (You know nothing about what happens after the ball makes contact with the ground, so there's no point in addressing anything that might happen after that point).
answer/question/discussion:
It will look like it is falling direct and downward
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Your instructor is trying to gauge the typical time spent by students on these questions. Please answer the following question as accurately as you can, understanding that your answer will be used only for the stated purpose and has no bearing on your grades:
Approximately how much time did you spend on this question?
20 min"
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Solution
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