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course Phy 201
Lab-related Questions for 101013Note: Before doing the lab questions you should run through the Sketching Exercise below. That exercise starts with questions about masses pulled upward by tension and downward by gravity, much along the lines discussed in class. It continues with questions related to masses on inclines.
In lab you timed the Atwood machine (paperclips on pulley) using your bracket pendulum.
`qx001. What was the length of your pendulum? What would be the period of a pendulum of this length, based on T = .2 sqrt(L)?
.4
you didn't give the length, but .4 sec period would be consistent with a 4 cm pendulum
it probably wasn't that short
`qx002. Give the time from release to first, second, third and fourth 'strikes' of the pendulum.
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2counts
3counts
4counts
5counts
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`qx003. In your first set of trials there were 3 large clips on each side.
In the first line give your counts for the first set of trials, separated by commas.
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12counts, 14counts, 15counts
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In the second line give the mean of your counts.
*******
13.67counts
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In the third line give the time interval in seconds which is equivalent to the mean of your counts.
**************
3seocnds
3.25seocnds
3.5seocnds
***************
In the fourth line give the acceleration corresponding to the time interval just reported.
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40/3=13.3cm/s
40/3.25=12.03cm/s
40/3.5=11.42cm/s
those would be average velocities, not average accelerations
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Starting in the fifth line give an explanation of the results you gave in the third and fourth lines.
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I just took the time I counted and turned it into seconds and then took the length of the atwood machine to find the accleration.
`qx004. In your second set of trials there were still 3 large clips on each side, but there was a small clip on the side which ascended in the first set.
In the first line give your counts for this set of trials, separated by commas.
************
11counts
12counts
11counts
*************
In the second line give the mean of your counts.
*********
11.3
**********
In the third line give the time interval in seconds which is equivalent to the mean of your counts.
*************
2.75 seconds
3seconds
2.75seconds
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In the fourth line give the acceleration corresponding to the time interval just reported.
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40/2.75=14.54cm/s
40/3=13.3cm/s
40/2.75=14.54cm/s
**********
You don't need to include an explanation, since the procedure is identical to that of the preceding questions, which you explained in answering that question. Just make sure your results make sense.
**************
Same as before
***************
`qx005. In the third set of trials a second small clip was added to each side.
In the first line give your counts for this set of trials, separated by commas.
***************
15counts
16counts
16counts
***************
In the second line give the mean of your counts.
15.6
In the third line give the time interval in seconds which is equivalent to the mean of your counts.
************
3.75counts
4counts
4counts
***************
In the fourth line give the acceleration corresponding to the time interval just reported.
***********
10.6cm/s
10cm/s
10cm/s
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`qx006. If there was a fourth set of trials, report as before:
************
I did not have a fourth set of trails
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In the first line give your counts for this set of trials, separated by commas.
In the second line give the mean of your counts.
In the third line give the time interval in seconds which is equivalent to the mean of your counts.
In the fourth line give the acceleration corresponding to the time interval just reported.
`qx007. For the trial with the greatest acceleration, sketch a force diagram showing, to scale, the tension and gravitational forces acting on the clips on the descending side of the system.
Which vector was longer?
************
Gravitational
***********
By what percent was it longer?
15%
What is the net force on these clips as a percent of the gravitational force?
65%
`qx008. For the trial with the greatest acceleration, sketch a force diagram showing, to scale, the tension and gravitational forces acting on the clips on the ascending side of the system.
Which vector was longer?
**************
Gravitiational
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By what percent was it longer?
12%
What is the net force on these clips as a percent of the gravitational force?
40%
you have to have accelerations to answer this question
then by figuring the accelerations as a percent of the acceleration of gravity, you have a good idea of how the tension and gravitational force vectors differ
`q009. At what average rate does the acceleration of the system change with respect to the number of small paperclips?
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2:1
Im not really for sure what the question is asking
you will need to get the accelerations
then carefully apply the definition of ave rate of change to the present question, in order to see what needs to be divided by what
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`q010. How much acceleration do we tend to be gaining, per added paperclip?
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Within a couple of cm/s
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`q011. The unbalance in the gravitational forces with each new paperclip is of course significant. It is this unbalance that causes the differences in the system's acceleration.
The total mass of the system does increase slightly with each added small paperclip, but for the moment let's assume that the resulting change in the total mass of the system isn't significant.
What percent of the acceleration of gravity do we get from each added small clip?
*************
15%
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How is this related to the mass of a single clip as a percent of the system's total mass?
***********
Because it adds to the system and helps slows It down.
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What is your conclusion about the ratio of the mass of a large clip to the mass of a small clip?
***********
The larger paper clip slows the system down faster than the small one.
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`q012. This question can be challenging. Don't let yourself get too bogged down on it:
In the preceding you drew conclusions based on the assumption that the changes in the system's total mass due to adding up to a few small paperclips was insignificant. It is perfectly possible that uncertainties in measuring the time intervals were large enough to obscure the effect of the changes in the total mass.
However refine your answers to the preceding question to take account of the change in total system mass.
(One possible approach: assume that the requested ratio is r and symbolically solve for the acceleration a in terms of the number N of added small clips, sketch a graph showing the predicted shape of your a vs. N curve, and see what value of r best matches this graph with a graph of your observed a vs. N).
Sketching exercise
The figure below is a free body diagram for a mass m on one side of an Atwood machine. The sketch is considered to be to scale.
`q`s001. Sketch the tension and gravitational forces, head-to-tail, and sketch the net force F_net. Keep your sketch to scale and estimate the following:
|| T || as a percent of || m g ||
45%
|| F_net || as a percent of || m g ||
45%
|| F_net || as a percent of || T ||
75%
note: || R || represents the magnitude of the vector R. The magnitude of a vector is always positive, unless the magnitude is zero. The magnitude can never be negative.
`q`s002. According to the sketch below:
|| T || as a percent of || m g ||
35%
|| F_net || as a percent of || m g ||
35%
|| F_net || as a percent of || T ||
75%
`q`s003. If || F_net || is equal to || m g ||, then the acceleration of the mass must be equal to g, since || m g || / m = || g ||.
In the figure above, is the magnitude of the acceleration of the mass greater, equal to, or less than the magnitude of the acceleration of gravity?
Greater than
Estimate the acceleration of the mass as a percent of the acceleration of gravity.
55%
The acceleration of gravity is 980 cm/s^2. What therefore is your estimate of the magnitude of the acceleration of this mass.
`q`s004. In the sketches above:
Will the mass accelerate in the upward or downward direction?
Downward
If the mass is known at a certain instant to be moving upward, is it speeding up or slowing down?
Speeding up
If the mass is known at a certain instant to be slowing down, then is it moving upward or downward?
Downward.
The next sketch shows a series of five situations. The situations will be referred to as A, B, C, D, and E, from left to right.
`q`s005. In which of the situations A, B, C, D and E is the mass accelerating upward?
B
`q`s006. In which of the situations would the mass have to be traveling downward in order to be slowing down?
A.
`q`s007. In which of the situations is the magnitude of the acceleration of the mass greater than the magnitude of the acceleration of gravity?
C.
`q`s008. Estimate the magnitude of each acceleration as a percent of the acceleration of gravity. Give your estimates in order, in one line separated by commas, from A through E. Starting in your second line give at least a brief explanation of how you arrived at your estimates.
A. 35%
B. 15%
C.95%
D.98%
E.99%
`q`s009. Estimate the acceleration of the mass in each figure, in cm/s^2. You are asked to estimate the acceleration, not the magnitude of the acceleration, so each answer should be + or -. Assume the downward direction to be positive.
A.-
B.+
C.+
D.-
E.-
`q`s010. The figure below depicts a mass on an incline. The x axis is sketched parallel to the incline, and the vector indicating the weight m g of the object is assumed to be in the vertical downward direction.
Make your own sketch, as close to that of the figure as possible.
Sketch the projection lines used in projecting the weight vector onto the x and the y axes.
Estimate the magnitude of the x projection as a percent of || m g ||
45%
Estimate the magnitude of the y projection as a percent of || m g ||
25%
If the x projection is the net force on the object, what is your estimate of its acceleration in cm/s^2?
45%
`q`s011. Estimate, as percents of m g, the magnitudes of the x and y components of the vector m g depicted in the figure below (it's not labeled by m g is the red vector).
Do your percents add up to 100? Should they?
55%
45%
`q`s012. Estimate, as percents of m g, the magnitudes of the x and y components of the vector m g depicted in the figure below (it's not labeled by m g is the red vector).
Do your percents add up to 100? Should they?
x=80%
y=20%
`q`s013. For each of the three figures below sketch an object on the incline, an x-y coordinate system with x axis parallel to the incline, and a vector m g depicting the weight of the object.
For each of your figures estimate the magnitudes of the x and y components of your m g vector as percents of m g.
Give your results in three lines. Each line should consist of your estimate of the x component, and of the y component. Starting in the fourth line give a bit of explanation.
x=75%
y=25%
x=65%
y=35%
x=55%
y=45%
I am not really for sure if I done this correctly I just draw the lined where I thought it went and done the prcentage line.
`q`s014. In the figure below the cart has mass m and the suspended mass is .25 m.
If the incline was level and frictionless the net force on the system would be .25 m g, the total mass 1.25 m and the acceleration would be F_net / mass = .25 m g / (1.25 m) = .2 g, or about 200 cm/s^2.
However, there's that incline. So sketch your x and y axes, with the x axis parallel to the incline. Project m g onto the x axis and estimate the magnitude of your projection as a percent of m g. Using this estimate:
Specify your chosen positive direction for the system, give your expression for the net force, and explain how got that net force.
Using your expression for the net force and the total mass of the system, give the resulting acceleration of the system.
"
You really need to get those accelerations for the Atwood machine.
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