phy121
Your 'cq_1_02.2' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.
** **
Assignment 2
Seed Question 2.1
________________________________________
The problem:
A graph is constructed representing velocity vs. clock time for the interval between clock times t = 5 seconds and t = 13 seconds. The graph consists of a straight line from the point (5 sec, 16 cm/s) to the point (13 sec, 40 cm/s).
• What is the clock time at the midpoint of this interval?
answer/question/discussion:
The clock time at the midpoint is 9 seconds. I added the beginning and ending times, and divided by 2 to get the midpoint.
What is the velocity at the midpoint of this interval?
answer/question/discussion:
The velocity is constant over the graph, so change in distance/change in time gives us 24/8, or 3 cm/second.
The velocity isn't constant. The two points represent very different velocities.
Your calculation does have a meaning, but the result is not a velocity.
The number 24 has units, as well as a meaning, as does the number 8.
I believe that 24 is the numerical value of the change in the velocity, and 8 is the numerical value of the change in clock time.
When you divide the change in velocity by the change in clock time, you don't get the velocity.
• How far do you think the object travels during this interval?
answer/question/discussion:
We subtract the starting position from the ending position to determine the distance traveled. 40cm – 16 cm = 24 cm.
40 cm is not a quantity associated with the problem, nor is 16 cm.
40 cm/s and 16 cm/s are given quantities, but cm/s and cm are very different quantities with different meanings.
• By how much does the clock time change during this interval?
answer/question/discussion:
We subtract start time from end time to determine change in clock time. In this case,
13cm-5cm=8cm
• By how much does velocity change during this interval?
answer/question/discussion:
Velocity in this interval is constant at 3 cm/second
• What is the average rate of change of velocity with respect to clock time on this interval?
answer/question/discussion:
I believe velocity does not change on this interval.
• What is the rise of the graph between these points?
answer/question/discussion:
The rise of this graph is the change in y, or 24.
• What is the run of the graph between these points?
answer/question/discussion:
The run of this graph is the change in x, or 8.
• What is the slope of the graph between these points?
answer/question/discussion:
The slope of the graph is rise/run, or 24/8, or 3.
• What does the slope of the graph tell you about the motion of the object during this interval?
answer/question/discussion:
The slope of the graph is equal to the average velocity over the length of the graph.
• What is the average rate of change of the object's velocity with respect to clock time during this interval?
answer/question/discussion:
I do not believe the velocity changes with respect to clock time.
** **
20 minutes
** **
See my notes, which hopefully aren't too cryptic; they are intended to clarify some important ideas about units and about identifying the quantities you are given.
You are really doing pretty well here and should have no trouble identifying and correcting your errors. I suggest you do think through my notes before you look at the given solutions in the link below:
&#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. &#