# Question Video: Calculating Wave Speed Physics • 9th Grade

A sound wave in a particular object has a frequency of 260 Hz and a wavelength of 2.5 m. At what speed does the sound wave propagate in that object, to the nearest meter per second?

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### Video Transcript

A sound wave in a particular object has a frequency of 260 hertz and a wavelength of 2.5 meters. At what speed does the sound wave propagate in that object to the nearest meter per second?

Let’s begin by writing down the values that we’ve been given here. We already know that the object has a frequency represented by 𝑓 of 260 hertz and a wavelength 𝜆 of 2.5 meters. Now to answer this question, recall that we can relate the frequency and wavelength of a wave to its speed 𝑠 using the formula 𝑠 equals 𝑓 times 𝜆. Since we already have values for both of the terms on the right-hand side of the formula, let’s go ahead and substitute them in. Frequency times wavelength gives us 260 hertz times 2.5 meters. But before we calculate, let’s take a moment to think about the units here.

Recall that hertz has base SI units of inverse seconds. And if we choose to write our frequency value like this, it’s easier to see how this formula combines units of per seconds with units of meters to give us a final value in meters per second, which is a good sign because we are solving for a speed. All that’s left to do now is calculate. And 260 times 2.5 comes out to exactly 650. This value is already written to the nearest meter per second, so we have our answer. The sound wave in this object travels at a speed of 650 meters per second.