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course Phy 201
I really did not understand how to do the last part of the questions, if you could give me some more input in what you want, that would be great. Thank you
Magnets and cars
A car with a magnet on the end was brought into proximity with an opposing magnet and released. The distance traveled by the car was observed as a function of proximity.
The car was also timed as it coasted to rest over a variety of distances.
In some experiments the opposing magnet was brought into proximity with the car, which was free to accelerate as soon as the magnets were sufficiently close.
In some experiments the car was permitted to roll down an incline into proximity with a fixed magnet; the release point, distance of closest approach and rebound distance up the ramp were observed
In some variations two cars with opposing magnets were released simultaneously and distances from release point observed.
Insert a copy of your data here, along with any previously submitted work you wish to include:
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1st magnet move 35 cm in about 2.5 seconds
2nd = 32 cm in about 2 seconds
Mass of car 15 grams
Opposing magnet with in a fingers width 18 cm in about 1.5 seconds
1st attempt
V0= 0cm/sec
Vf= 14cm/sec
d'v = 14 cm/sec
a= 5.6cm/sec^2
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Based on your observations:
As the car coasts across the tabletop:
What is its acceleration?
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5.6 cm/sec^2
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You need to show how you got this. Calculating in my head I get something close to double this, but I might be using a different trial that you are.
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How much frictional force is exerted per gram of the car’s mass?
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F=ma
F= 15 g (5.6 cm/s^2)
F= 84 g cm/sec^2
Fricional force = .84 g cm/s^2
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You got 84 g cm/s^2 above, now you have .84 g cm/s^2. You probably mean .84 g m/s^2, but 84 g cm/s^2 is OK for a 15 gram system.
That would be for 15 g. How much would it be for 1 gram? That's the energy per gram.
Note that the 5.6 cm/s^2 might not be right.
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How much work is done by friction per centimeter of coasting distance, per gram of the car’s mass?
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Your force-per-gram calculation would come out roughly 5 g cm/s^2 per gram.
Now if that force was exerted through 1 cm, how much work would it do?
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How much energy is dissipated by friction, per centimeter of coasting distance, per gram of the car’s mass?
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KE= 1/2mv^2
KE= 7.5 (196)
KE= 1470 joules
Wnet = 1470/35cm = 42 joules/cm
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Your mass is in grams, your velocity in cm/s. The units of that calculation don't come out in Joules.
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Pick one of your trials. How much energy was dissipated by frictional forces for this trial, and what was the initial proximity of the magnets?
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18 cm in 1.5 sec
V0= 0 cm/sec
Vf= 12 cm/sec
a= 8 cm/sec^2
F= 120 g*cm/sec^2
Force before has to equal force afterwards
KE=1/2 mv^2
KE= 1/2(15g)(12cm/s^2)
KE= 1080 joules
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Right idea. But 12 cm/s is the average velocity, not the initial velocity. You'll want to correct that.
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Also the units don't come out in Joules. A Joules is a N * m, or kg m^2 / s^2. Your calculation comes out in g cm^2 / s^2, which is ergs.
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Graph coasting distance vs. proximity, and relabel your graph to show the energy dissipated by friction vs. the initial proximity of the magnets.
Partition your horizontal axis at half-centimeter intervals and find the slopes associated with the corresponding trapezoids.
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What is the meaning of the slope of a typical trapezoid?
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Make a table of trapezoid slope vs. the midpoint of the corresponding proximity interval, and sketch the corresponding graph.
What is the meaning of your graph?
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Divide your graph into trapezoids at half-cm intervals and determine the area of each.
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What is the meaning of the area of a typical trapezoid?
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If you were to measure magnet force vs. magnet proximity you could construct a graph of force vs. proximity. Based on this graph how could you obtain a graph of the potential energy of the magnet system vs. proximity?
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Self-critique (if necessary):
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Self-critique rating:
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It looks like you only used 1 distance of separation, which you indicates as a finger's width. Looks like good data, but to graph energy vs. separation you need more than one separation.
You'll be OK here if you just correct the calculations you've done, Check my notes.
Once more this will be good practice for the test.
&#Please see my notes and, unless my notes indicate that revision is optional, submit a copy of this document with revisions 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.
If my notes indicate that revision is optional, use your own judgement as to whether a revision will benefit you. &#
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