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Carnegie Mellon University



Problem 29 Medium Difficulty

Two trains on separate tracks move toward each other. Train 1 has a speed of $1.30 \times 10^{2} \mathrm{km} / \mathrm{h} ;$ train $2,$ a speed of 90.0 $\mathrm{km} / \mathrm{h}$ . Train 2 blows its horn, emitting a frequency of $5.00 \times 10^{2} \mathrm{Hz}$ . What is the frequency heard by the engineer on train 1 ?


596 $\mathrm{Hz}$


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Aina N.

October 24, 2020

A stone weighs 450 N in air and 200 N in water. Calculate the volume of stone. *

Video Transcript

So here we have a we don't have a stationary observer or a source. Both the source and the observer are in motion. Therefore, we can say the observed frequency would be the frequency of the source multiplied by the speed of sound. Plus, the frequents felt the speed of the observer divided by the freak, the velocity speed of sound minus the velocity of the source. And so because each train is moving towards each other, the velocity of the observer is greater than zero and the velocity of the source is greater than zero. So we can then say that the speed of the source which would be trained to would be 90 kilometers per hour and we could just convert two meters per second, says to be 1000 meters per kilometer and then multiplying this by one hour for every 3600 seconds. And this is giving us 25.0 meters per second and from this week and then say that velocity of the observer is 130 kilometers per hour. Let's convert again, multiplied by one hour for every 3600 seconds, and this was giving us 36 0.1 meters per second. So the observed frequency will be equaling. 500 hertz multiplied by 343 meters per second plus 36.1 meters per second, divided by 343 meters per second, minus 25.0 meters per second. And we find that the observed frequency is equaling 596 hertz. This would be our final answer. That is the end of the solution. Thank you for watching.

Carnegie Mellon University
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