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Phy 201
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: ->->->->->->->->->->->-> :
The force of the child tossing it is acting on it upward, while gravity is acting downward on it.
@& The force exerted by the child ends at the instant of release. The only force acting during the specified interval is the gravitational force.*@
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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 speed of the ball decreases until it reaches its highest point, then increases 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: ->->->->->->->->->->->-> :
The path of the ball would appear elyptical or near circular. It would not be straight up and down since there is movement forward.
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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: ->->->->->->->->->->->-> :
The path would be the same unless the bicycle was moving at a faster pace. If the kid did not catch the ball it would appear to land behind him or behind his hand.
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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: ->->->->->->->->->->->-> :
During the interval, the speed of the ball will become greater, while accelerating at the acceleration of gravity. 9.8m/s2.
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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: ->->->->->->->->->->->-> :
From the perspective of the child, the path will appear to travel towards the back of the car. From the outside of the car, the path will appear straight down.
@& If you were 10 feet in front of the dropping point would you expect the ball to come in your direction? It would do so, having a forward speed equal to the speed of the car. So it doesn't drop straight down.
It is this forward speed that would result in a force of air resistance and cause the ball to appear to the child to move backwards. At low speed the air resistance would be insignificant and the ball would appear to the child to drop straight down.*@
@& See also the discussion below; again revision is not required.*@
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&#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. &#