course phy 121 ŁԱassignment #004 004. `Query 4 Physics I 06-15-2008
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23:31:44 Intro Prob 6 given init vel, accel, `dt find final vel, dist If initial velocity is v0, acceleration is a and time interval is `dt, then in symbols what are the final velocity vf and the displacement `ds?
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RESPONSE --> Use a = dv /dt to solve for dv dv = a*dt vf = v0 + dv vf = v0 + (a*dt) To find ds we first have to find vAve. vAve = (v0 + vf) / 2 vAve = [v0 + (v0 + (a*dt)) / 2 ds = vAve * dt confidence assessment: 2
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23:32:50 **You would use accel. and `dt to find `dv: a * `dt = `dv. Adding `dv to initial vel. vo you get final vel. Then average initial vel. and final vel. to get ave. vel.: (v0 + vf) / 2 = ave. vel. You would then multiply ave. vel. and `dt together to get the distance. For example if a = 3 m/s^2, `dt = 5 s and v0 = 3 m/s: 3 m/s^2 * 5 s = 15 m/s = `dv 15 m/s + 3 m/s = 18 m/s = fin. vel. (18 m/s + 3 m/s) / 2 = 10.5 m/s = vAve 10.5 m/s * 5 s = 52.5 m = dist. In more abbreviated form: a * `dt = `dv v0 + `dv = vf (vf + v0) /2 = vAve vAve * `dt = `ds so `ds = (vf + v0) / 2 * `dt. **
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RESPONSE --> self critique assessment: 3
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23:35:37 What is the displacement `ds associated with uniform acceleration from velocity v0 to velocity vf in clock time `dt?
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RESPONSE --> ds is associated with the area under the slope. In uniform acc from a velocity of v0 to vf the area will be a triangle under the slope. ds = vAve (the average height) * dt ( the distance across the base of the triangle. confidence assessment: 2
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23:36:31 ** Since accel is uniform vAve = (v0 + vf) / 2. Thus displacement is `ds = vAve * `dt = (v0 + vf) / 2 * `dt, which is the first equation of uniformly accelerated motion. **
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RESPONSE --> I didn't mention the equations, but I know and understand them pretty well. self critique assessment: 2
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23:46:38 Describe the flow diagram we obtain for the situation in which we know v0, vf and `dt.
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RESPONSE --> I use to think I was a visual-spatial learner, but in my last science class my professor had us using flow diagrams and they just don't make a lot of sense to me. I can decipher them, but I don't seem to be able to make them. But I can tell you: If we subtract the known v0 from vf we get the change in vel (dv). Multiply dv by the known dt and we get aAve. Add v0 and vf together and then divide by 2 we get the vAve. Take vAve and multiply by known dt and we get ds (if v0 equals 0, if not we have to figure the area of the rectangle under the triangle and add them togther). confidence assessment: 1
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23:50:56 ** The first level in the diagram would contain `dt, v0 and vf. Then v0 and vf would connect to `dv in the second level. The second level would also contain vAve, connected from vf in the first level to v0 in the first level. The third level would contain an a, connected to `dv in the second level and `dt in the first level. The third level would also contain `ds, connected to vAve in the fourth level and `dt in the first level. **
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RESPONSE --> That was a good description and I have drawn it out in my notebook. I believe I got all of the connections in my answer, but my attempt at drawing it originally doesnt look anything like that. self critique assessment: 2
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00:00:39 Query Add any surprises or insights you experienced as a result of this assignment.
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RESPONSE --> I am surprised that I can't draw a flow diagram. I think in pictures, I have always scored exceptionally high on spatial tests, for most of the problems we have done so far I have either drawn a picture or a graph in order to figure it out, but I can't draw a flow diagram. I make all of the connections, but I do it in a list of sorts down my paper. I work out each connection skip a line and do the next connection. confidence assessment: 3
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00:04:53 ** Student Response: I think I really confused what information stood for what in the Force and Pendulum Experiment. However, I enjoy doing the flow diagrams. They make you think in a different way than you are used to. INSTRUCTOR NOTE: These diagrams are valuable for most people. Not all--it depends on learning style--but most. **
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RESPONSE --> I think it is suitable to my learning style, but I am just too old to learn a new trick. I learned to organize my thoughts in outlines of sorts and have been doing it this way for MANY years. My husband tells me that they use them in his work all of the time. I will have to learn to use them when I teach, because they do help many students, but I don't personally like them. self critique assessment: 3
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