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The speed of sound in a certain metal is \(v_{m} .\) One end of a long pipe of that metal of length \(L\) is struck a hard blow. A listener at the other end hears two sounds, one from the wave that travels along the pipe's metal wall and the other from the wave that travels through the air inside the pipe. (a) If \(v\) is the speed of sound in air, what is the time interval \(\Delta t\) between the arrivals of the two sounds at the listener's ear? (b) If \(\Delta t=1.00 \mathrm{~s}\) and the metal is steel, what is the length \(L ?\)

Short Answer

Expert verified
The metal pipe is approximately 355 meters long.

Step by step solution

01

Understanding the Problem

When the pipe is struck, vibrations travel through the metal and the air inside the pipe at different speeds. The goal is to find the time difference between these vibrations reaching the listener.
02

Define Variables and Known Values

Let \( v_m \) be the speed of sound in the metal pipe, \( v \) be the speed of sound in air, and \( L \) be the length of the pipe. We need to find \( \Delta t \), the time difference when the two sounds arrive at the opposite end of the pipe.
03

Expression for Time Taken by Sound in Metal

The time taken by sound to travel through the metal, which we'll call \( t_m \), is given by:\[t_m = \frac{L}{v_m}\]
04

Expression for Time Taken by Sound in Air

The time taken by sound to travel through the air inside the pipe, denoted as \( t_a \), is:\[t_a = \frac{L}{v}\]
05

Calculate Time Interval \( \Delta t \)

The time interval \( \Delta t \) between the arrivals of the two sounds is the difference between \( t_a \) and \( t_m \):\[\Delta t = t_a - t_m = \frac{L}{v} - \frac{L}{v_m} = L \left( \frac{1}{v} - \frac{1}{v_m} \right)\]
06

Solve for Length \( L \) Given \( \Delta t \) and Steel

Given \( \Delta t = 1.00 \, \text{s} \). Speed of sound in steel \( v_m \approx 5960 \, \text{m/s} \) and speed of sound in air \( v \approx 343 \, \text{m/s} \). Substitute these into the equation:\[1 = L \left( \frac{1}{343} - \frac{1}{5960} \right)\]Solving for \( L \), we get:\[L = \frac{1}{\frac{1}{343} - \frac{1}{5960}} \approx 355 \, \text{meters}\]
07

Conclusion

The length of the pipe is approximately 355 meters when the time interval \( \Delta t \) between sounds through steel and air is 1 second.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Speed of Sound in Metal
When sound travels through a medium, its speed is determined by the medium's physical properties. In the case of metal, sound waves can propagate quite quickly due to the dense and tightly packed atomic structure. This structure allows vibrations to pass efficiently from particle to particle. As a general rule, sound travels faster in solids than in gases.

For instance, in steel, the speed of sound is approximately 5960 meters per second. This high speed is due to the metal's strong intermolecular forces and its ability to transmit vibrations with little resistance. This concept is crucial when determining how fast sound will reach a listener from one end of the metal to the other. The speed of sound in metals like steel is vastly higher compared to that of air.

Understanding this characteristic of metals helps us calculate how long it will take for sound to travel a particular distance and, consequently, the time interval between sound waves traveling through different mediums.
Speed of Sound in Air
Sound waves move significantly slower in air compared to solids like metal. This difference is primarily because air molecules are spaced further apart than those in a solid, resulting in slower transmission of energy between particles. In typical atmospheric conditions, the speed of sound in air is about 343 meters per second.

The speed of sound in air can be influenced by factors such as temperature and pressure. Warmer temperatures tend to increase the speed, while cooler temperatures slow it down. In the context of the exercise, knowing the exact speed of sound in air lets us determine how much longer it will take for sound to travel the same distance through air compared to metal.

This discrepancy directly affects the time interval between when sounds are heard through different mediums, making the speed of sound in air a critical piece of the puzzle when solving related problems.
Time Interval Calculation
The time interval calculation is the key step in understanding how and when sounds are heard from different mediums. When a sound is generated at one end of a pipe, it travels at different speeds through the metal of the pipe and the air inside it. This results in the listener hearing two sounds at separate times.

To find the time interval \( \Delta t \) between these two sounds, we start by calculating the time taken for sound to travel through each medium:
  • Through metal: \( t_m = \frac{L}{v_m} \)
  • Through air: \( t_a = \frac{L}{v} \)
The difference, \( \Delta t = t_a - t_m \), gives us the time interval we're seeking. This interval depends on the speed of sound in each medium and the length of the pipe, enabling us to solve for the unknown variable if necessary. For example, with a known \( \Delta t \), as in our original scenario, solving for \( L \), the length of the pipe, becomes a straightforward mathematical exercise.

In summary, understanding how sound waves travel through different materials and calculating their arrival times correctly can provide valuable insights into physical properties and dimensions of the structures involved.

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Most popular questions from this chapter

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