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===Quick links=== ==This wiki== * [[start|Main classwiki page]] * [[CLASS INFORMATION|Class Info]] * {{:Kuzma_Syllab_Spr2014_v4.pdf|Syllabus}} * [[FREQUENTLY ASKED QUESTIONS|FAQ]] * [[CLASS MATERIALS|Class materials]] * [[PHYSICS LABORATORY|Labs]] * [[|Schedule]] * [[PHYSICS WORKSHOP|Workshop]] * {{:workshops:ph299_syllabus_14sp.pdf|W/S syllabus}} * [[Computational Projects|Projects]] * [[White noise project|White noise]] * [[Rainbow project|Rainbow]] * [[Digital sound project|Digital sound]] * [[Announcements]] ==Earlier material== * [[Chapter 13]] * [[Chapter 14]] * [[Exam 1 review]] * [[Chapter 25]] * [[Chapter 26]] * [[Chapter 27]] * [[Exam 2 review]] * [[Final exam review]] ==Previous wikis== * [[|Ph202 - 2014]] ==Other learning tools== * [[|University D2L site]] * [[|Text & homework]] \\ <sub><color magenta>PH203KUZMASPRING2014</color></sub> ==Knowledge & computation== * [[|Wolfram]] $\alpha$ * [[wp>Physics_portal|Wikipedia]] * [[|Physical constants]] * [[| The Physics Hypertextbook]] * [[| HyperPhysics]] ==Add more by editing:== * [[sidebar|This sidebar]] * [[Tasks to do]] ==Help for editors== * [[doku>wiki:syntax|Help on wiki codes]] * [[|Help on wiki math]] * [[Tips on editing]] =="Sandboxes" for practice== * [[Draft page|Practice here]] * [[Draft page 2|Or here if locked-out]]


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=====Practice/work here if other pages are temporarily locked by other editors===== ---- ===Problem Two pendulums (or, //pendula//) are made of identical 1 kg masses suspended on two weightless strings, 40.0 and 40.5 cm in length. If these pendulums are deflected from vertical by 5 cm and released at the same time, how long will it take for them to get completely "out of step" with each other? Steps: - Convert **relevant** quantities to SI units: * $l_1$ = 40.0 cm = 0.400 m * $l_2$ = 40.5 cm = 0.405 m * masses and (small) deflections are irrelevant for finding periods and timing of oscillations - Find each period: * $T_1=2\pi\sqrt{\frac{l_1}{g}}$ $\approx 6.283\sqrt{\frac{0.400\,{\text m}}{9.8\,\frac{\text m}{ {\text s}^2}}}=1.269\,$s * $T_2=2\pi\sqrt{\frac{l_2}{g}}$ $\approx 6.283\sqrt{\frac{0.405\,{\text m}}{9.8\,\frac{\text m}{ {\text s}^2}}}=1.277\,$s - By the time $t$ the two pendulums are "out of step", one would have completed an extra 1/2 periods compared to the other: * $t = \left(n+\frac{1}{2}\right)T_1=nT_2$ {{ :figs:lec01fg4.png?nolink|}} - Use this relationship to solve for $n$, then find $t$: * first, open the parentheses: $t= nT_1+\frac{1}{2}T_1=nT_2$ * then, isolate $n$ by combining terms: $\frac{1}{2}T_1=nT_2-nT_1=n\,(T_2-T_1)$ * lastly, $n=\frac{T_1}{2(T_2-T_1)}$ $=\frac{1.269\,{\text s}}{2\,\cdot\,8\times 10^{-3}\,{\text s}}$ $=79$ * $t=nT_2$ $=79\cdot1.277\,{\text s}\approx 100\,$s - Make sense of the answer: * This is much longer than the periods of oscillations, but short enough to observe the effect before the oscillations die down due to friction ====Homework Questions Ch.13==== ---- ===Problem 54 part B=== <color #5555BB>A 0.550-kg block slides on a frictionless horizontal surface with a speed of 1.10m/s . The block encounters an unstretched spring and compresses it 21.0cm before coming to rest. For what length of time is the block in contact with the spring before it comes to rest? (Your actual numbers may vary)</color> * I looked at the homework solutions posted in D2L and for the solution, I don't understand why it states that "the period corresponds to one-fourth of a period." Where does the 1/4-th come from? I know that the spring was compressed 0.25 m so are we assuming that the period is originally 1 meter and that's where the 1/4 comes from? * If you are trying to map the motion described in the problem onto an oscillation, then, at the beggining, when the encounter happens, the potential energy of the spring is zero (unstretched spring), that means you start at an equilibrium point. When the block comes to rest, its velocity (and so its kinetic energy) is zero, that means you end up at the $x_\text{max}$ (maximum distance from equilibrium) position. Since a typical oscillation cycle goes like this: $0 \rightarrow x_\text{max}\!\rightarrow 0 \rightarrow -x_\text{max}\!\rightarrow 0...$ etc, the time between successive zeros (passing the equilibrium point) is half the period, and the time between a zero (equilibrium point) and $x_\text{max}$ is half that, or 1/4 period. If you plot a $\sin(x)$ function, it will be obvious. So, this is how you get 1/4 period. {{ :figs:lec01fg7.png?nolink |}}

draft_page_2.1396725146.txt.gz · Last modified: 2014/04/05 19:12 by wikimanager