# PH202 Recitation Week 09 Problem Set Winter 2015

## Transcription

PH202 Recitation Week 09 Problem Set Winter 2015

PH202 Recitation Week 09 Problem Set Winter 2015 Ryan Scheirer Email: [email protected] My Website: http://people.oregonstate.edu/~scheirer/PH202_REC.html Problem 01 Figure 1.a shows the displacement of particles in a string as a function of position x at time t = 0s. Figure 1.b shows the displacement of the particle at x=0 as a function of time. (a) Determine the wavelength, period, wavenumber, frequency and amplitude. (b) Write the equation for the displacement of this traveling wave as a function of position and time. Problem 02 Autofocus features on cameras can be classified into two categories, active and passive. Passive autofocusing utilizes software to determine how to adjust the lenses in the camera, most smart phones use this technique. While active autofocusing determine the distance to the object using very high frequency (ultrasonic) sound waves, or infrared laser light. In 2014 the first smart phone LG G3 was released with the capability to use active autofocuing with infrared light. (a) Assume standard atmospheric conditions, what is the total time it takes for an active sound pulse camera to emit a sound and receive it if the object of interest is 10 meters away? (b) How long would it take for a light pulse to travel the same distance? 1 Problem 03 You decide to drop a stone off a cliff of unknown height. The splash of the object hitting the water below is heard 3.5 seconds after you dropped the stone. How high is the cliff? Problem 04 While playing an intense game of Robot Roller-Derby Disco Dodgeball, I realized that the sound intensity level was quite high, around 90 dB. If the area of my eardrum is about 5.0 × 10−5 m2 , (a) how much energy is absorbed by the eardrum per second? (b) At this rate, how many hours of RRDDD would I have to play for my eardrum to receive a total energy of 1.0 J? Problem 05 Two sound sources each emit power uniformly in all directions. There are no reflections. Both sources are located on the x axis, one at the origin and the other at x= 186 m. The source at the origin emits four times more power than the other source. (a) Find the two positions along the x-axis where the two sounds are equal in intensity. (b) The source located at the origin emits 400 W, what are the sound level intensities of the two locations found in part a? Problem 06 In the figure below, the power power of source 1 is 10 W. What is the sound level intensity at the origin? 2