00:01
That if a speaker mounted on an automobile broadcast a song with what speed, and it wants us to give this speed in kilometers per hour, does the automobile have to move towards a stationary listener so that the listener hears the song with each musical note shifted up by one note in comparison to the song heard by the automobile driver.
00:22
On the equally tempered chromatic scale, the ratio of frequencies of the neighboring notes is two to the 112th.
00:28
So i wrote that what we have here then what we're given is that f is equal to f times 2 to the 112th also we know that the speed of sound and we're going to assume that its normal room temperature is 343 meters per second okay so well we have one ratio of f prime to f we also know that f prime this new frequency is equal to f times the ratio of 1 over 1 minus the velocity of the source, the automobile in this case, divided by the speed of sound, c.
01:12
Okay.
01:14
Well, then if we solve for the velocity of the source, the velocity of the automobile, we find that v .s is equal to 1 minus 1 divided by 2 to the 112 multiplied by c.
01:33
So if we plug in our value for c into this equation, we find that this is equal to 19 .25 meters per second.
01:46
But we are asked to give our answer in kilometers per hour...