quiz6_sp10_sol

# quiz6_sp10_sol - Physics 101 Classical Physics Spring 2010...

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Physics 101 Classical Physics Spring 2010 Quiz 6 Instructions : The answer sheets must be handed in as soon as time is called. You have until 9:20am. Answer the following two multiple choice questions. Each question is worth 5 points. 1. A traveling wave is described by y ( x, t ) = A cos( kx - ωt ) . The wavelength of the wave is λ = 2 / 3 m, its period is T = 8 s, and its amplitude A = 1 m. At x = 1 / 4 m and t = 1 s, which of the following is the speed of a point on the wave, in the y direction? (a) 16/3 m/s (b) 12 m/s (c) π/ 4 m/s (d) 0 m/s (e) 1 m/s The question is asking about the speed in the y direction, not the x direction, so we can’t use v = λf . Instead, we need to take the derivative of y ( t ) to get v y = dy/dt . So we have dy dt = ωAsin ( kx - ωt ) We also have k = 2 π λ = 6 π 2 rad / m, ω = 2 π T = π 4 rad / s. Plugging everything in we have dy dt = π 4 rad / s(1 m ) sin (3 π 1 4 - π 4 ) = π 4 m / s sin( 3 π 4 - π 4 ) = π 4 m / s . So the answer is

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## This document was uploaded on 05/20/2010.

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quiz6_sp10_sol - Physics 101 Classical Physics Spring 2010...

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