Phy 201
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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 downward force of gravity and the force of the car moving forward.
The automobile exerts no force on the falling ball.
• 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:
It slows down as it increases in height until it stop momentarily at the maximum height then it slowly speeds up as it falls until it stops when caught. This forms a curved graph.
• Describe the path of the ball as it would be observed by someone standing along the side of the road.
answer/question/discussion:
It forms a curved path beginning at the point of release traveling up then curving and traveling downward ending at the same height as the release.
• 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 curve would probably be steeper because on a bike it would travel less distance than in the car in the same time frame.
The curve would be longer on the side where the ball is falling because it moves further in the negative vertical direction.
• 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 speed will increase as it falls. The acceleration=9.8m/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. (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 will see the ball drop straight down. Observers will see the ball fall at an angle toward the rear of the car.
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20min
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Most of your answers were good, but there were some misconceptions. See the link and submit a revision if you have question or aren't sure of your understanding.
&#At least part of your solution does not agree with the solution and comments given at the link below. You should view the solution at that link and self-critique as indicated there.
Solution
This link also expands on these topics and alerts you to many of the common errors made by students in the first part of this course. &#