Giancoli 7th Edition textbook cover
Giancoli's Physics: Principles with Applications, 7th Edition
11
Vibration and Waves
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11-1 to 11-3: Simple Harmonic Motion
11-4: Simple Pendulum
11-7 and 11-8: Waves
11-9: Energy Transported by Waves
11-11: Interference
11-12: Standing Waves; Resonance
11-13: Refraction
11-14: Diffraction

Question by Giancoli, Douglas C., Physics: Principles with Applications, 7th Ed., ©2014, Reprinted by permission of Pearson Education Inc., New York.
Problem 40
Q

A cord of mass 0.65 kg is stretched between two supports 8.0 m apart. If the tension in the cord is 120 N, how long will it take a pulse to travel from one support to the other?

A
0.21 s0.21 \textrm{ s}
Giancoli 7th Edition, Chapter 11, Problem 40 solution video poster
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VIDEO TRANSCRIPT

This is Giancoli Answers with Mr. Dychko. The speed of a wave on a cord is going to be square root of the tension in the cord divided by its mass per unit length. And so μ can be replaced with m divided by l. And FT divided by m over l is the same as FT times l over m because we can multiply top and bottom by l and these l's cancel here, we're left with an l multiplied by the thing on top. So, speed is square root tension times length divided by mass of the cord. The time it takes to go from one end of the cord to the other is going to be that distance which is l divided by the speed. And instead of dividing by this we're going to multiply by its reciprocal. So, it's going to be l multiplied by square root of m over FT l. And this, you know, this works out to l over square root l times square root m over FT, you can think of it that way. And this is square root l. And I put that underneath the square root sign. So, we have time as square root m l over tension force. So, that's 0.65 times 8 meters divided by 120 newtons which is 0.21 seconds.

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