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:
Force of gravity
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 slows as it goes to the bottom of the roof then speeds back up on its way down to the hands.The acceleration of
gravity is pulling against the ball on the way up and the force of gravity pulls it down on the wy down
Describe the path of the ball as it would be observed by someone standing along the side of the road.
answer/question/discussion:
It would go up then come back down into his hands.It would not move backwards enough for a person standing along sid ethe
road to notice
A ball tossed at a speed which keeps it from hitting the roof will not exceed a speed of about 4 m/s, around 10 mph. If the car is moving at 10 mph, the observer at the side of the road will see the ball moving faster in the horizontal direction and in the vertical direction, even when it's vertical speed is greatest. When the ball is moving slowly near the top of its path, its motion will be almost all in the horizontal direction.
The path of the ball will turn out to be parabolic, has observed from the side of the road.
As observed from the side of the road the ball travels forward at constant speed as it rises then falls.
The ball speeds up in the vertical direction but not in the horizontal.
The path is therefore curved--in fact it can be shown that the path is parabolic.
The ball is observed from the roadside to speed up in the vertical direction but not in the horizontal, causing the path to curve (as it turns out the path is in fact parabolic).
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 ball would go up then backwards away from the direction of the bike. It would not fall back into his hands
As observed by the child, the ball would tend to accelerate a bit in the direction opposite motion, because of air resistance. Unless the child is moving pretty fast, and/or the ball is of pretty low density, the deviation in the motion is not likely to be noticeable, and the child will perceive the ball is traveling pretty much straight up and down. The path deviation due to a little air resistance will be less than the inevitable deviation from one toss to the next (i.e., nobody tosses the ball perfectly every time, so there's always a give of deviation for which to adjust).
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 speed up because the acceleration of gravity
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:
It will go opposite of the direction of the car but will not be noticed much. The observer will probably see a greater
increase in the ball gong backwards because of the side view.
If you drop the ball out of the window, it doesn't end up going backwards with respect to the road. The ball might slow down a bit, due to air resistance (which is being ignored here), but it continues to move forward as it falls, and after hitting will bounce down the road in the direction of the car's motion until it strikes an obstacle.
To an observer along the side of the road, it moves forward and a pretty constant velocity as it falls faster and faster, resulting in a parabolic path.
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15min
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&#Good work. See my notes and let me know if you have questions. &#