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 instant it is released, gravitational force starts acting downward on the ball. The momentum force continues throughout the path of the ball. And a normal force acts by the childs hand when the ball is caught.
The gravitational force is always present; after release it is the only significant force acting on the ball. Change in momentum is the result of a force; momentum is not a force.
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 ball is moving upward at a decreasing speed until it reaches its maximum height. At that time the ball begins to fall downward, increasing speed with time until the ball is caught, at which time it will stop.
Describe the path of the ball as it would be observed by someone standing along the side of the road.
answer/question/discussion: a parabolic shape would appear to have been travelled by the ball.
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: the path would look the same if he were on a bike since he is still moving forward when the ball is thrown and caught. If he neglects to catch the falling ball, it would continue to increase speed until it hits the ground.
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 falling from the roof to the floor of the car would still increase speed with the acceleration of gravity. It would also appear to be moving forward from a stationary point of view outside of the car.
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: as seen by the child, and taking wind resistance into effect, the ball would appear to be falling, but also moving backwards away from him, towards the back of the car. As seen by a viewer on the side of the road, the ball would appear to have a curved path, moving forward, but decreasing that movement with increase in time.
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20 min.
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&#This looks good. See my notes. Let me know if you have any questions. &#