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: ->->->->->->->->->->->-> :
#$&* The force of gravity act on the ball, as well as the horizontal force from the car moving forward.
Motion is not associated with force. Acceleration is; an object subject to 0 net force has 0 acceleration, so its velocity is constant.
• What happens to the speed of the ball between release and catch? Describe in some detail; a graph of speed vs. clock time would also be appropriate.
answer/question/discussion: ->->->->->->->->->->->-> :
#$&* Once the ball is released, the ball has its greatest speed. The ball will continue to rise until it reaches its max height, at which point the ball will have a speed of zero. Then the ball will fall due to the force of gravity and once it reaches the height at which the ball was released, it will have the same initial speed (unless other forces acted upon it).
• Describe the path of the ball as it would be observed by someone standing along the side of the road.
answer/question/discussion: ->->->->->->->->->->->-> :
#$&* I imagine that since the car is moving forward, the ball will travel in an arch-like pattern if someone was to be observing from the road.
• How would the path differ if the child was coasting along on a bicycle? What if the kid didn't bother to catch the ball? (You know nothing about what happens after the ball makes contact with the ground, so there's no point in addressing anything that might happen after that point).
answer/question/discussion: ->->->->->->->->->->->-> :
#$&* If the child was to be on a bike, I imagine the ball would have the same general motion pattern, however there would be just less of an arch.
• 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: ->->->->->->->->->->->-> :
#$&* The ball would most likely descend at the speed of gravity once released. It would be traveling at 9.8 m/s every second.
• What if the child holds the ball out of an open window and drops it. If the ball is dense (e.g., a steel ball) and the car isn't moving very fast, air resistance will have little effect. Describe the motion of the ball as seen by the child. Describe the motion of the ball as seen by an observer by the side of the road. (You know nothing about what happens after the ball makes contact with the ground, so there's no point in addressing anything that might happen after that point).
answer/question/discussion: ->->->->->->->->->->->-> :
#$&* The child dropping the ball would see the ball shoot back horizontally once dropping the ball. An observer from the street would only see a ball drop straight down after being released from the child’s hand.
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about 15 minutes
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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: ->->->->->->->->->->->-> :
#$&* If they are moving 10m/s and the ball was in the air for 0.5sec, the ball should have moved 5 meters.
• As observed by a passenger in the car, what was the path of the ball from its release until the instant it was caught?
answer/question/discussion: ->->->->->->->->->->->-> :
#$&* I believe the ball is released, and then drifts backwards as descends back to the child’s hand.
• 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: ->->->->->->->->->->->-> :
#$&* The ball would look as if it were traveling in an arch-like pattern.
• How fast was the ball moving in the vertical direction at the instant of release? At that instant, what is its velocity as observed by a line of people standing along the side of the road?
answer/question/discussion: ->->->->->->->->->->->-> :
#$&* I would have to guess that the ball was moving 10m/s since that is how fast the car and child were moving.
• How high did the ball rise above its point of release before it began to fall back down?
answer/question/discussion: ->->->->->->->->->->->-> :
#$&* Using the acceleration of 9.8m/s^2 and it’s time in the air of 0.5 seconds, I think the ball reached a max height of 4.9 meters.
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about 15 minutes
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&#Please compare your 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. &#