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course phy 201
0905 1AM
`q001. This series of questions uses the basic analysis of a straight-line v vs. t graph for an object which starts from rest:Sketch a v vs. t graph representing the motion of a ball that starts from rest and moves for 6 seconds, averaging a velocity of 15 cm / sec.
Describe your graph.
My graph is increasing at a constant rate.
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What are the initial and final velocities of the ball?
The initial velocity is 0 cm/sec and the final velocity is 30 cm/sec
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What is its velocity at the 3-second mark?
15cm/sec
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By how much does its velocity change during the 6-second time interval?
It changes by 30cm/sec
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How quickly is its velocity changing during the 6-second interval? Note that the answer to this question is also the slope of your v vs. t graph.
5cm/sec
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Right idea. However if you divide 30 cm/s by 6 s you get 5 cm/s^2, not 5 cm/s.
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`q002. This question asks you to do something closely related to today's class, but somewhat different from anything we actually did.
How far does the ball in the preceding question travel during the 6 second interval?
The average speed is 5cm/sec and it rolls for 6 seconds so it goes 30 cm.
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The average velocity is 15 cm/s, not 5 cm/s.
5 cm/s^2 is the average rate at which the velocity is changing.
30 cm/s is the final velocity, but the displacement is not 30 cm.
The average velocity and time interval would tell you how far the object travels.
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How far does it travel during the first 3 seconds?
15cm
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This isn't all that far off, but I don't think you reasoned it out correctly. Can you explain your reasoning?
My suggestion would be to first figure out what the average speed would be for the first 3 seconds, and go from there.
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Would a sketch of its position vs. clock time be a straight line, a rising curve with an increasing slope, a rising curve with a decreasing slope, or some other type of curve?
Since it starts at rest and ends going 30cm/sec and has a set slope it will be a straight line.
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Its velocity vs. clock time graph will be a straight line.
However the question asked about a graph of position vs. clock time.
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`q003. Report your data from today's experiment. Your report should be clear and concise, telling the reader what was measured and how, and specifically what the results were.
A 30 cm long ramp was placed on two stacks of dominos that varied slightly in height by an unknown amount. A metal ball or marble was then placed on one end and nudged with an unknown amount of force and was timed with a pendulum how long it to took reach the other end of the ramp. From left to right it took the ball 2.5 oscillations to reach 30 cm. From right to left it took the ball 2 oscillations to reach the end. From the following information the average velocity for both trials was obtained by dividing the change in position with the change in clock time. This case the position was in cm and the clock time was in oscillations.
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`q004. For one of your ramps, indicate the displacement of the ball and the number of cycles of your pendulum corresponding to motion to or from rest in one direction, and the displacement of the ball and the number of cycles to or from rest in the other direction.
I answered this question in the summery of the last question.
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What is the average velocity of the ball as it travels in each direction, according to your data? Your time will be measured in cycles of the pendulum, rather than in seconds. A cycle is a perfectly valid unit of time, as long as you know the length of the pendulum. So for example the average velocity of the ball will be in centimeters / cycle. We can later convert the result to units involving seconds.
According to my data for the first trial with the ball going from left to right the average velocity was 12cm/sec. For the second trial with the ball going from right to left the average velocity was 15cm/sec.
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What are the initial and final velocity of the ball in each direction?
Initial velocity of the ball in both cases was 0cm/sec. The final velocity of the ball going from left to right was 30cm/2.5 oscillations and from right to left it was 30cm/2 oscillations.
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Those would be the average velocities, each being a displacement divided by a time interval. You would get average velocities of 12 cm/oscillation and 15 cm/oscillation.
What would be the two corresponding final velocities?
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What is the change in velocity in each direction?
From both directions the change in velocity was from 0cm/osc to 30cm/osc
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The trials had different average velocities, so they would have different final vfelocities and hence different changes in velocity.
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How quickly did velocity change in each direction? Note that an answer to this question is also the slope of an appropriate v vs. t graph.
From left to right the velocity changed 12cm/osc and from right to left the velocity changed 15cm/osc.
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Those are average velocities. To figure out how quickly the velocity changed, you would have to use the change in velocity and the change in clock time.
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Self-critique (if necessary):
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Self-critique rating:
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You've got a good start, but you still need to sort out a couple of these ideas.
&#Please see my notes and submit a copy of this document with revisions, comments and/or questions, and mark your insertions with &&&& (please mark each insertion at the beginning and at the end).
Be sure to include the entire document, including my notes. &#
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