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Phy 231
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 throw and gravity
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@& The force of the throw has had its effect prior to release; after release there is no residual force of the throw. The ball's initial upward velocity is of course due to the throw, and as time goes on other forces do influence its motion.*@
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 ball speeds up comes to rest then speeds up again as it
falls.
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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 ball would go up while moving foward then fall down.
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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 rider would need to throw the ball in front of him a little
so they could catch it. If they didn't catch it then it would hit
the ground.
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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 initial speed will be 0 the acceleration will be g*m and the
final will be Intial v + a * t
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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: ->->->->->->->->->->->-> :
The ball will look as though it is falling backwards to the
child. To the observer the ball will fall straight but the car
will keep moving.
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** **
15 min
** **
7/30/11
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: ->->->->->->->->->->->-> :
5 m
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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: ->->->->->->->->->->->-> :
The ball went up and fell back 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: ->->->->->->->->->->->-> :
It would appear that the ball was moving foward as it rose and
then fell back down.
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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: ->->->->->->->->->->->-> :
9.8 m/sec^2 * 0.25sec
= 0.2 m/sec
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@& 9.8 * .25 = 2.45, not .2.*@
How high did the ball rise above its point of release before it
began to fall back down?
answer/question/discussion: ->->->->->->->->->->->-> :
x-x0 = 0.5(v0 + vf) * t
ds = 0.5 * (0.2 m/sec) * 0.25 sec
ds = 0.025 m
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@& Right, if the .2 m/s had been right*@
*#&!
@&
&#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. &#
*@