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PHY 121
Your 'cq_1_17.1' 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: ->->->->->->->->->->->-> :
gravity, velocity of the car and its contents, air resistance
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Gravity and air resistance are forces.
The velocity of the car is not a 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: ->->->->->->->->->->->-> :
It is released from 0 cm/s, it rises upward from the force of the push, it gradually slows because of the pull of gravity and comes to a momentary rest. Gravity continues to work on the ball to pull it back down to the child's hand.
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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: ->->->->->->->->->->->-> :
From the side of the road, the path of the ball would look like a small hill.
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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: ->->->->->->->->->->->-> :
If the child were on a bike, you would not have the same everything moving together inside momentum, so the path would be sharper--more of a straight up. If the kid didn't bother to catch the ball, it would go straight up (or close to straight up) and then down to 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: ->->->->->->->->->->->-> :
If the child drops the ball from the inside roof to the floor of the car, the speed of the ball will increase toward the floor as the ball accelerates at the rate of 9.8 m/s^2 from the pull of gravity.
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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 child will see the ball go straight down to the ground, however since the car is moving, it will seem to the child like the ball went backward. An observer would see the ball go straight down to the ground under the influence of gravity.
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The ball will continue moving at the speed of the car, at least until air resistance slows it slightly.
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*#&!
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Solution
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