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PHY 121
Your 'cq_1_18.1' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.
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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: ->->->->->->->->->->->-> :
Gravitational force, as well as the force exerted on the ball by the child.
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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: ->->->->->->->->->->->-> :
It is increases at a decreasing rate. Once it reaches the peak, it starts to pick up speed until it is caught.
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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: ->->->->->->->->->->->-> :
It will appear to go up, peak, and return to the child. Since it is in a moving car, it will also seem to have moved further down the road, relative to their position.
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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: ->->->->->->->->->->->-> :
There would be no difference in the position of the ball. The child's position may be different but the ball will return to him, assuming the distance thrown is short. If he fails to catch the ball, it will fall to the ground, and he will continue forward on his bike.
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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: ->->->->->->->->->->->-> :
Speed will increase until it makes impact with the floor of the car.
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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: ->->->->->->->->->->->-> :
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It will not fall straight to the ground if the car is moving, even at a slow pace. It will have some horizontal motion involved. The child will see the ball disappear, since he is moving forward. THe ball will continue to be further behind him as he continues forward.
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15 minutes
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A child in a car tosses a ball upward so that after release it requires 1/2 second to rise
and fall back into the child's hand at the same height from which it was released. The car
is traveling at a constant speed of 10 meters / second in the horizontal direction.
Between release and catch, how far did the ball travel in the horizontal direction?
answer/question/discussion: ->->->->->->->->->->->-> :
Since the car is moving at 10m/sec, the ball will move 5m in the horizontal direction in 0.5 second.
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As observed by a passenger in the car, what was the path of the ball from its release until
the instant it was caught?
answer/question/discussion: ->->->->->->->->->->->-> :
An observer in the car would see the ball go straight up, then straight down.
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Sketch the path of the ball as observed by a line of people standing along the side of the
road. Describe your sketch. What was shape of the path of the ball?
answer/question/discussion: ->->->->->->->->->->->-> :
A parabola, with the peak upward.
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How fast was the ball moving in the vertical direction at the instant of release? At that
instant, what is its velocity as observed by a line of people standing along the side of
the road?
answer/question/discussion: ->->->->->->->->->->->-> :
Speed in vertical direction will depend on the force placed upon it by the child. The velocity of the ball will appear to be the same as the car from people standing by the road.
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How high did the ball rise above its point of release before it began to fall back down?
answer/question/discussion: ->->->->->->->->->->->-> :
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*#&!
@& Good answer to most of these questions.
Do check out the discussions at the links given below. No need for any revision unless you have questions.
&#See any notes I might have inserted into your document, and before looking at the link below see if you can modify your solutions. If there are no notes, this does not mean that your solution is completely correct.
Then please compare your old and new solutions with the expanded discussion at the link
Solution
Self-critique your solutions, if this is necessary, according to the usual criteria. Insert any revisions, questions, etc. into a copy of this posted document. Mark any insertions with &&&& so they can be easily identified.If your solution is completely consistent with the given solution, you need do nothing further with this problem. &#
&#See any notes I might have inserted into your document, and before looking at the link below see if you can modify your solutions. If there are no notes, this does not mean that your solution is completely correct.
Then please compare your old and new solutions with the expanded discussion at the link
Solution
Self-critique your solutions, if this is necessary, according to the usual criteria. Insert any revisions, questions, etc. into a copy of this posted document. Mark any insertions with &&&& so they can be easily identified.If your solution is completely consistent with the given solution, you need do nothing further with this problem. &#
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