#$&*
Phy 241
Your 'cq_1_18.1' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.
** **
A child in a slowly moving car tosses a ball upward. It rises to a point below the roof of the car and falls back down, at which point the child catches it.
During this time the car neither speeds up nor slows down, and does not change direction.
What force(s) act on the ball between the instant of its release and the instant at which it is caught? You can ignore air resistance.
answer/question/discussion: ->->->->->->->->->->->-> :
Gravity
#$&*
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 kid is point A.
The roof is point B
The kid releases the ball from point A to B the velocity of the ball decreases.
From point B to A the velocity of the ball increases
A graph of speed vs clock time would look a parabola concave up
#$&*
Describe the path of the ball as it would be observed by someone standing along the side of the road.
answer/question/discussion: ->->->->->->->->->->->-> :
It would look like half an ellipse concave down.
#$&*
@&
Good, but the graph would actually be a parabola.
*@
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: ->->->->->->->->->->->-> :
I would look more like a semi-circle, rather than an ellipse, becuase the bicycle is slower. If the kid doesnt bother to catch it, it would look like
a semi-circle concave down, but at the point he doesnt catch it, there would be a tangle line the ball would follow
#$&*
@&
Again right idea, though the path would actually be a parabola.
*@
What if the child drops the ball from the (inside) roof of the car to the floor? For the interval between roof and floor, how will the speed of the ball change?
What will be the acceleration of the ball? (You know nothing about what happens after the ball makes contact with the floor, so there's no point in addressing
anything that might happen after that point).
answer/question/discussion: ->->->->->->->->->->->-> :
If the child drops the ball FROM the roof of the car, the speed of the ball would increase and the acceleration of the ball would increase as well.
#$&*
@&
The ball doesn't get significantly closer to the center of the Earth so the gravitational force doesn't change significantly, nor does the ball's mass change. So the ball's acceleration doesn't change.
*@
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: ->->->->->->->->->->->-> :
If the child drops the ball out the window the child would see the ball fall away from the child in a horizontal and vertical direction
The bystander would see the same thing but from a different angle. To the bystander the ball would move along the graph of a line similiar to -sqrt(-t)
#$&*
** **
20 minutes
** **
11/25/2011 815pm
A child in a car tosses a ball upward so that after release it requires 1/2 second to rise and fall back into the child's hand at the same height from which
it was released. The car is traveling at a constant speed of 10 meters / second in the horizontal direction.
Between release and catch, how far did the ball travel in the horizontal direction?
answer/question/discussion: ->->->->->->->->->->->-> :
So in 1/2 a second the ball rose and fell. That means the ball traveled 5 meters. Of course to the child, the ball did move horizontally at all.
#$&*
As observed by a passenger in the car, what was the path of the ball from its release until the instant it was caught?
answer/question/discussion: ->->->->->->->->->->->-> :
sorta like half of an ellispe concave down
#$&*
Sketch the path of the ball as observed by a line of people standing along the side of the road. Describe your sketch. What was shape of the path of the ball?
answer/question/discussion: ->->->->->->->->->->->-> :
sorta like half an ellipse concave down
#$&*
How fast was the ball moving in the vertical direction at the instant of release? At that instant, what is its velocity as observed by a line of people
standing along the side of the road?
answer/question/discussion: ->->->->->->->->->->->-> :
'dt = .25s
a = -9.81 m/s^2
a = 'dv/'dt
'dv = a*'dt
= -9.81 m/s^2 * .25s
= -2.45 m/s
It would actually be positive because the kid is throwing the ball. so there would be a positve velocity of 2.45 m/s
the vertical velocity by the bystanders would be the same, but since the car is moving, the ball would look like its moving too
So the ball has a horizontal velocity as well of 10 m/s
v = sqrt[(2.45m/s)^2 + (10m/s)^2]
= 10.3 m/s
#$&*
How high did the ball rise above its point of release before it began to fall back down?
answer/question/discussion: ->->->->->->->->->->->-> :
v_ave = 'ds/'dt
'ds = v_Ave*'dt
= (2.45/2) m/s*.25s
= 0.31 m
#$&*
*#&!*#&!
@&
Good, but see my notes.
Also it's best to submit only one 'seed' question at a time. I need to be able to identify which question is which in order to append the appropriate links.
In this case I'm pretty sure the two questions are at the two links given below. Be sure to read those discussions. No revision is required.
&#See any notes I might have inserted into your document, and before looking at the link below see if you can modify your solutions. If there are no notes, this does not mean that your solution is completely correct.
Then please compare your old and new solutions with the expanded discussion at the link
Solution
Self-critique your solutions, if this is necessary, according to the usual criteria. Insert any revisions, questions, etc. into a copy of this posted document. Mark any insertions with &&&& so they can be easily identified.If your solution is completely consistent with the given solution, you need do nothing further with this problem. &#
&#See any notes I might have inserted into your document, and before looking at the link below see if you can modify your solutions. If there are no notes, this does not mean that your solution is completely correct.
Then please compare your old and new solutions with the expanded discussion at the link
Solution
Self-critique your solutions, if this is necessary, according to the usual criteria. Insert any revisions, questions, etc. into a copy of this posted document. Mark any insertions with &&&& so they can be easily identified.If your solution is completely consistent with the given solution, you need do nothing further with this problem. &#
*@