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On December 26, 2004, a great earthquake occurred off the coast of Sumatra and triggered immense waves (tsunami) that killed some 200,000 people. Satellites observing these waves from space measured 800 km from one wave crest to the next and a period between waves of 1.0 hour. What was the speed of these waves in m/s and in km/h? Does your answer help you understand why the waves caused such devastation?

Short Answer

Expert verified
The tsunami waves traveled at 222.22 m/s or 800 km/h, explaining their destructive power.

Step by step solution

01

Identify Key Variables

We need to identify the key variables that we will use to solve for wave speed. The problem gives us the wavelength \( \lambda \) of 800 km and the period \( T \) of 1.0 hour.
02

Convert Units

To find speed in m/s, first convert the wavelength from kilometers to meters: \( 800 \text{ km} = 800,000 \text{ m} \). Also, convert the period from hours to seconds: \( 1.0 \text{ hour} = 3600 \text{ seconds} \).
03

Use the Wave Speed Formula

The formula for wave speed \( v \) is \( v = \frac{\lambda}{T} \), where \( \lambda \) is the wavelength and \( T \) is the period. Substitute the converted values: \[ v = \frac{800,000 \text{ m}}{3600 \text{ s}} \].
04

Calculate Wave Speed in m/s

Now calculate the speed: \( v = \frac{800,000}{3600} \approx 222.22 \text{ m/s} \).
05

Convert Wave Speed to km/h

Convert the speed from m/s to km/h by multiplying by the conversion factor 3.6 (since 1 m/s is equal to 3.6 km/h). Thus, \( 222.22 \text{ m/s} \times 3.6 = 800 \text{ km/h} \).
06

Interpret the Results

The wave speed is very high at 222.22 m/s (or 800 km/h), indicating why the tsunami caused such massive devastation, as it delivered a large amount of energy over a vast area quickly.

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Key Concepts

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

Tsunami Waves
Tsunamis are huge ocean waves typically generated by underwater earthquakes, volcanic eruptions, or landslides. These waves are known for their incredible speed and energy, traversing entire ocean basins with minimal energy loss. The 2004 Sumatra earthquake-induced tsunami is an example of their destructive power. Despite their immense size, while traveling in the deep ocean, tsunami waves may only be a meter high. However, as they approach shallow coastal areas, their speed decreases, and the waves grow significantly taller, leading to devastating impacts on coastlines.
Understanding the mechanics of tsunami waves is crucial in improving warning systems and minimizing the damage in future events.
Unit Conversion
Unit conversion is an essential aspect of solving physics problems involving real-world scenarios like tsunami wave calculations. In our exercise, we begin by converting the wavelength from kilometers to meters, given that scientific and engineering calculations typically use SI units. Converting kilometers to meters is simple: multiply by 1,000, as 1 kilometer equals 1,000 meters.
  • Wavelength: 800 km = 800,000 m
Next, convert the period from hours to seconds. There are 3,600 seconds in an hour, so multiply the number of hours by 3,600 to convert.
  • Period: 1 hour = 3,600 seconds
Such conversions are pivotal because they ensure consistency in units, allowing for accurate calculations.
Wavelength and Period
Wavelength and period are fundamental characteristics of waves. Wavelength, denoted as \( \lambda \), refers to the distance between consecutive wave crests. The exercise describes the wavelength as 800 km. The period, \( T \), is the duration it takes for one complete wave to pass a specific point, given as 1 hour here.
The relationship between these properties and wave speed is encapsulated in the formula: \[ v = \frac{\lambda}{T} \]This formula tells us that speed is directly proportional to wavelength and inversely proportional to the period. Understanding these elements not only aids in computing wave speed but also in grasping how waves behave as they travel across different mediums.
Energy of Waves
The energy carried by waves, particularly tsunamis, is vast and impactful. It's this energy that causes significant changes to landscapes and affects human settlements upon hitting coastlines. The energy of a wave is generally a function of its amplitude, speed, and the density of the water it travels through. Tsunamis, even though initially generated with small amplitudes in deep waters, transfer enormous amounts of energy over long distances.
Once a tsunami reaches shallower regions, its speed decreases, and wave height increases, concentrating the energy and causing large-scale destruction. This understanding helps in developing better protective measures against future tsunami events, emphasizing the importance of wave properties and energy in assessments.

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Most popular questions from this chapter

A certain transverse wave is described by $$y(x, t) = (6.50 \, \mathrm{mm}) \mathrm{cos} \, 2\pi \Big( \frac{x}{28.0 \mathrm{cm}} - \frac{t}{0.0360 \, \mathrm{s}} \Big)$$ Determine the wave's (a) amplitude; (b) wavelength; (c) frequency; (d) speed of propagation; (e) direction of propagation.

In your physics lab, an oscillator is attached to one end of a horizontal string. The other end of the string passes over a frictionless pulley. You suspend a mass \(M\) from the free end of the string, producing tension \(Mg\) in the string. The oscillator produces transverse waves of frequency \(f\) on the string. You don't vary this frequency during the experiment, but you try strings with three different linear mass densities \(\mu\). You also keep a fixed distance between the end of the string where the oscillator is attached and the point where the string is in contact with the pulley's rim. To produce standing waves on the string, you vary \(M\); then you measure the node-to-node distance \(d\) for each standingwave pattern and obtain the following data: (a) Explain why you obtain only certain values of \(d\). (b) Graph \(\mu d^2\) (in kg \(\cdot\) m) versus \(M\) (in kg). Explain why the data plotted this way should fall close to a straight line. (c) Use the slope of the best straight-line fit to the data to determine the frequency \(f\) of the waves produced on the string by the oscillator. Take \(g = 9.80 \, \mathrm{m/s}^2\). (d) For string A (\(\mu = 0.0260\) g/cm), what value of \(M\) (in grams) would be required to produce a standing wave with a node-to-node distance of 24.0 cm? Use the value of \(f\) that you calculated in part (c).

One string of a certain musical instrument is 75.0 cm long and has a mass of 8.75 g. It is being played in a room where the speed of sound is 344 m/s. (a) To what tension must you adjust the string so that, when vibrating in its second overtone, it produces sound of wavelength 0.765 m? (Assume that the breaking stress of the wire is very large and isn't exceeded.) (b) What frequency sound does this string produce in its fundamental mode of vibration?

With what tension must a rope with length 2.50 m and mass 0.120 kg be stretched for transverse waves of frequency 40.0 Hz to have a wavelength of 0.750 m?

A heavy rope 6.00 m long and weighing 29.4 N is attached at one end to a ceiling and hangs vertically. A 0.500-kg mass is suspended from the lower end of the rope. What is the speed of transverse waves on the rope at the (a) bottom of the rope, (b) middle of the rope, and (c) top of the rope? (d) Is the tension in the middle of the rope the average of the tensions at the top and bottom of the rope? Is the wave speed at the middle of the rope the average of the wave speeds at the top and bottom? Explain.

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