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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: ->->->->->->->->->->->-> :
Gravity and the force of the childs strength.
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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 horizontal velocity of the ball should be constant (neglecting air resistance), the vertical velocity will be greatest initially, approach 0, then speed up again as it falls back down.
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Describe the path of the ball as it would be observed by someone standing along the side of the road.
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The ball would just appear to go up and straight back down, though it is actually moving forward in a horizontal direction as well.
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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: ->->->->->->->->->->->-> :
I believe the path would be the same on a bicycle, though there would be less air resistance
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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 acceleration of the ball should be -9.8m/s^2
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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 would see the ball fall backward and downward, maybe in a diagonal direction because he is still moving forward, away from the ball. An observer on the side of the road may only see the ball fall straight downward, MAYBE with the slightest backward movement from air resistance.
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If the child drops the ball just as he passes you, the ball will fall to the ground while moving away from you in the direction of the car. It will never move back toward you. To the child it might appear that the ball falls downward and backward, because air resistance will slow the ball while the car does not slow, but to anyone standing alongside the road the ball will always move in the direction of the car (even if the car appears to edge out in front of it).
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5 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: ->->->->->->->->->->->-> :
If the car is moving at 10m/s and the ball traveled for half of one second, the ball should travel 5 meters in the horizontal direction.
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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: ->->->->->->->->->->->-> :
Straight up and straight 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: ->->->->->->->->->->->-> :
the shape of the path of the ball should be a long, stretched out parabola with a very small slope.
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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?
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maybe 1m/s? As observed from the side of the road, I suppose it would appear to be faster as the car drives by them. Maybe 6m/s?
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The ball's speed changes by 9.8 m/s evey second, so in 1/2 second the ball's vertical speed will change by 1/2 of 9.8 m/s, or 4.9 m/s. Going up, it slows by 4.9 m/s, coming to rest. So it had to start with an upward velocity of 4.9 m/s. Coming back down it speeds up by 4.9 m/s, so it returns to the child's hand at 4.9 m/s.
From the side of the road the ball is observed to start upward at 4.9 m/s while is moves forward at 5 m/s. That is, its velocity is a vector with components having magnitudes 5 m/s and 4.9 m/s. What therefore are the magnitude and direction of the ball's initial velocity?
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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: ->->->->->->->->->->->-> :
0.5m?
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You know the ball's acceleration, final velocity and the duration of the interval from release to its maximum height. You can reason out the vertical displacement, or you can find it using equations (you should be able to do this both ways).
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Good start, but some things need to be revised.
&#Please see my notes and submit a copy of this document with revisions, comments and/or questions, and mark your insertions with &&&& (please mark each insertion at the beginning and at the end).
Be sure to include the entire document, including my notes. &#
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