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.
The forces that act on the ball are Fw, and Fn.
F_w is presumably the weight of the ball, the force exerted by gravity. As long as the ball is in the near vicinity of the Earth's surface this foce will be present, so it should indeed be listed.
It isn't clear what you mean by F_n or what the source of this force would be between the instant of release and the instant at which the ball is caught.
answer/question/discussion:
• 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.
The ball’s initial velocity will be the same velocity when it is caught by the child. As soon as the ball is throw it decelerates at a rate of 9.8m/sec^2 until it reaches 0. Then it heads in the other direction because gravity takes over.
answer/question/discussion:
• Describe the path of the ball as it would be observed by someone standing along the side of the road.
The ball would have two motions: horizontal and vertical. Vertically the ball would go up and down, the maximum velocities are equal when the ball is released and it hits the child’s hand. Horizontally the ball goes at the same velocity as the car. It follows directly above the child.
answer/question/discussion:
• 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?
If the child was coasting along a bicycle, vertically the same would happen. Horizontally the ball would land a little farther ahead of the child. This is because the frictional force causes the boy to slow down. If he did not bother to catch it the ball would hit the ground and bounce in the same direction that the boy is coasting.
answer/question/discussion:
• What if the child drops the ball from the roof 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?
The acceleration of the ball will be 9.8m/sec^2. The ball will speed up until it hits the ground.
answer/question/discussion:
• 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.
The ball will travel at the same velocity as the car until it hits the ground. When this happens, the ball will bounce in the same direction, but the friction on the ground will cause the ball to slow down.
answer/question/discussion:
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10 minutes
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Good, except for one important issue you need to address.
Note also that there is a 'seed' question 17.2. I just discovered it had not been posted on the Assignments page and just now corrected the error. It involves some important vector calculations and it would be a good idea for you to go back and do it.
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