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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Assignment 18 Seed Question 1
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 forces that act on the ball between the time the child releases it and the time it is caught will be that of gravity as well as the muscle force exerted by the child. Such muscle force will cause the ball to stop and resists the ball’s path of movement. Thus, the muscle acts as a preventive force (or a force that acts opposite of that of the direction of motion).
• 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: Speed is similar to velocity, but velocity is a vector. If we look at the fact that vf= 0 m/s when the ball is at its highest point in the air, we can describe the speed of the ball as being the highest when it leaves the child’s hand and when it return to the child’s hand, whereas the speed is at its lowest when the ball is at its highest point (when it stands as still for a moment). Thus, a graph of speed vs. clock time would look very much so like a parabola, or an arc. The ball’s speed would start off high, then get lower, then get higher again. Thus, the arc would open upward.
Since acceleration is uniform v vs. t is linear, so | v | vs. t is piecewise linear. The graph would be much as you describe, but instead of being parabolic, it will be V shaped, consisting of two straight segments.
• Describe the path of the ball as it would be observed by someone standing along the side of the road.
answer/question/discussion: Someone alongside the road would see the path of the ball similar to the way the graph looks, as the car is in motion. IF the car was standing still, the ball would appear to be going up and coming down in a fairly straight shaped sort of line. However, since the car is moving, the ball will move slightly with it in an arc sort of shape.
• 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?
answer/question/discussion: If the child was coasting along on a bicycle, he or she would have had a very similar path to that of the path from the car. This is because the ball was still thrown from a moving object/vehicle. If the child did not catch the ball, the path of the ball (displacement) would have gone down farther but would have followed the same downward motion. However, the difference would be that the ball would pick up speed.
• 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?
answer/question/discussion: IF the child drops the ball, then the v0 starts out at 0 m/s and the vf would then have the highest velocity/speed. The direction of motion then changes as well, as when it was thrown the initial direction was up and then the downward motion set in. Here, the initial direction of the motion is downward. The acceleration of the ball will be the force of gravity, as there are no other forces acting on the ball. Thus, the acceleration will be 9.8 m/s^2.
• 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.
answer/question/discussion: If the child holds the ball out of an open window, then the drop of the ball will follow a motion that appears to be a direct, downward, vertical drop from the view of the child. To be more specific, the child’s view will not really see the motion from the building where the ball was dropped if looking downward. From the view of the side street stander, it would seem that the ball follows a straight path, from top to bottom of the window to the ground, vertically.
The ball speeds up in the vertical direction but not in the horizontal. The path is therefore curved--in fact the path is parabolic.
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It took me about 25 mins to do this.
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&#Good work. See my notes and let me know if you have questions. &#