A friend of yours is loudly singing a single note at 400 Hz while racing toward you at 25.0 m/s on a day when the speed of sound is 340 m/s. a. What frequency do you hear?

Video transcript

Welcome back, everyone. We are making observations about a whistle that is on the bike of a motorcycle rider. We are told that the frequency of the whistle is 2.5 times 10 to the third Hertz or 2. kilohertz. We are told that the velocity of sound through the air at that instant in time is 342 m per second. And we are then told that the bike rider is approaching an observer at kilometers per one hour. And we are tasked with finding the frequency heard by that very observer. Now, the sound of the whistle is going to undergo the Doppler effect. So we can use the formula of our initial frequency times one minus the velocity of the rider divided by the velocity of the air. Of course, plugging in our terms. We need to make sure everything's in the correct units. And what we need is everything in meters per second, four hour velocities. So let me go ahead and convert the velocity of our rider here. We know that in one kilometer there is 1000 m and in one hour there's 3600 seconds which when you multiply straight across, we get that the velocity of the rider is 18 point oh six m per second. Now, we are ready to find the frequency heard by the observer. This is going to be 2.5 times 10 to the third times one minus 18 point oh six divided by 342, giving us a final answer of Hertz corresponding to our answer. choice of c Thank you all so much for watching. I hope this video helped. We will see you all in the next one.