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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: ->->->->->->->->->->->-> :
gravitional, child tossing the ball, movement of the car,
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only the gravitational force is present once the ball is released
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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: ->->->->->->->->->->->-> :
Upon releae the speed of the ball is increasing until it reaches its max height; at max height speed is 0.
Speed will increase downward after max height has been reached.
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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 car is moving slowly therefore once the ball is thrown up it will appear to 'fall behind' the car. Once it reaches max height, the ball should stop
then come back down until the ball is caught.
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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 will appear no different than the car. The ball will increase in speed until it hits the ground whereas it would have stopped where the kid caught it.
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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 ball will have an acceleartion of 9.8m/s^2 until it hits the ground.
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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 fall straight down if it is heavy enough, this will be the same observation from side or top.
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20 mins
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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: ->->->->->->->->->->->-> :
h'ds=10m/s*.5s=5m
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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: ->->->->->->->->->->->-> :
it should appear as a slight curve increasing at at decreasing rate until max height then stopping,
then coming downward at a increasing rate until it is caught.
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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: ->->->->->->->->->->->-> :
The sketch would have a parabolic shape.
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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: ->->->->->->->->->->->-> :
.5=’dt
2.45 m/s in the vertical direction and 10m/s horizontal
sqrt(10 m/s^2+2.45 m/s^2)=10.3m/s by onlookers or magnitude.
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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: ->->->->->->->->->->->-> :
Vave is 2.45/2=1.225m/s so times .25s= 0.306m
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25 mins
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&#This looks very good. Let me know if you have any questions. &#