#$&*
Phy 121
Your 'cq_1_13.1' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.
** CQ_1_13.1_labelMessages **
Copy the problem below into a text editor or word processor.
• This form accepts only text so a text editor such as Notepad is fine.
• You might prefer for your own reasons to use a word processor (for example the formatting features might help you organize your answer and explanations), but note that formatting will be lost when you submit your work through the form.
• If you use a word processor avoid using special characters or symbols, which would require more of your time to create and will not be represented correctly by the form.
• As you will see within the first few assignments, there is an easily-learned keyboard-based shorthand that doesn't look quite as pretty as word-processor symbols, but which gets the job done much more efficiently.
You should enter your answers using the text editor or word processor. You will then copy-and-paste it into the box below, and submit.
________________________________________
A ball rolls off the end of an incline with a vertical velocity of 20 cm/s downward, and a horizontal velocity of 80 cm/s. The ball falls freely to the floor 120 cm below.
• For the interval between the end of the ramp and the floor, hat are the ball's initial velocity, displacement and acceleration in the vertical direction?
The ball’s initial vertical velocity is -20cm/s because the ball is moving downward. The ball’s displacement in the vertical direction is -120cm and the acceleration in the vertical direction is -980cm/s^2 because of gravity.
#$&*
• What therefore are its final velocity, displacement, change in velocity and average velocity in the vertical direction?
The ball’s final vertical velocity is 0cm/s because it is hitting the floor below. The vertical displacement is -120cm. The change in velocity in the vertical direction is 20cm/s because 0cm/s- -20cm/s = 20cm/s. The average velocity in the vertical direction is -10cm/s.
#$&*
@&
The ball's final velocity will not be zero. The analysis ends at first contact with the floor, since at that instant acceleration ceases to be constant.
*@
• What are the ball's acceleration and initial velocity in the horizontal direction, and what is the change in clock time, during this interval?
The ball’s initial horizontal velocity is 80cm/s. The ball’s change in clock time during this interval is as follows:
vf = v0+a*’dt
0cm/s = 20cm/s+980cm/s^2*’dt
-20cm/s=980cm/s^2*’dt
.02s = ‘dt
Given that the change in time is .02s and with an initial horizontal velocity of 80cm/s and final velocity of 0cm/s because the ball hits the ground, we can now find the acceleration in the horizontal direction to be -4000cm/s^2 because:
vf = v0+a*’dt
0cm/s = 80cm/s+a*.02s
-80cm/s = a*.02s
-4000cm/s^2 = a
#$&*
• What therefore are its displacement, final velocity, average velocity and change in velocity in the horizontal direction during this interval?
The final horizontal velocity is 0cm/s because it is hitting the ground. The average velocity is 40cm/s because 0cm/s+80cm/s=80cm/s and 80cm/s / 2 = 40cm/s. The change in velocity is -80cm/s because 0cm/s-80cm/s=-80cm/s. The displacement is as follows:
‘ds = (vf+v0)/2*’dt
‘ds = (0cm/s+80cm/s)/2*.02s
‘ds = 80cm/s / 2 * .02s
‘ds = 40cm/s*.02s
‘ds = .8cm in the horizontal direction.
#$&*
• After the instant of impact with the floor, can we expect that the ball will be uniformly accelerated?
No we cannot expect that the ball will be uniformly accelerated.
#$&*
• Why does this analysis stop at the instant of impact with the floor?
This analysis stops the instant of impact because we do not have the required knowledge to further this analysis.
#$&*
*#&!
@&
You've based your analysis on the assumption that as it falls the ball accelerates uniformly from a speed of 20 cm/s to rest.
Based on this assumption your analysis is flawless.
However that assumption is not valid.
Check my notes, which I believe you will understand.
*@
@&
&#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. &#
*@