Lect_31_post - PHYS 221 Exam 2 S2016 140 Avg 120 100 80 60...

Info icon This preview shows pages 1–8. Sign up to view the full content.

View Full Document Right Arrow Icon
A B C D F Extra credit 0 20 40 60 80 100 120 140 3 6 9 12 15 18 21 24 27 30 33 36 39 42 45 48 51 54 57 60 63 66 69 72 75 78 81 PHYS 221 Exam 2 S2016 Avg
Image of page 1

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Lecture 31 Energy. Intensity. Interference. Beats.
Image of page 2
ACT: A sixth sense? A large ammunition factory and a town are separated by a rocky hill, at a horizontal distance of about 5 km. An accident produces a huge explosion in the middle of the night. What do the town folks experience? A. First the room shakes, and then they hear an explosion. B. First they hear an explosion, and then the room shakes. C. They hear an explosion and the room shakes at the same time.
Image of page 3

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
5 km Time for sound wave to reach the town: granite granite 6000 m/s Y v ρ Λ Ξ Μ Ο = = Μ Ο Ν Π Through hill (granite): 5000 m 0.8 s 6000 m/s x t v = = = This happened in California during WWII. Most people woke up (distressed…) to the light quake and then heard the explosion. Many attributed this to a sixth sense that had warned them of the imminent disaster. The sixth sense was just the laws of wave propagation… Through air: t = x v = 5000 m 343 m/s = 14.6 s 14 seconds later!
Image of page 4
Wave energy Work is clearly being done: F . dr > 0 as hand moves up and down. This energy must be moving away from your hand (to the right) since the kinetic energy (motion) of the end of the string grabbed by the hand stays the same. P
Image of page 5

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Transfer of energy The string to the left of x does work on the string to the right of x , just as your hand did: x Energy is transferred or propagated.
Image of page 6
Power Energy of a mass in SHM (attached to a spring k ) 2 2 2 1 2 E kA A ω = 2 k m ω Λ Ξ = Μ Ο Ν Π This energy propagates at speed v . the average energy per unit time that flows in the direction of propagation should be proportional to v 2 2 P v A ω For harmonic waves on a taut string (see appendix): P = 1 2 μ F ω 2 A 2 = 1
Image of page 7

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 8
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern