Frequency of the source

Ladies and gentlemen that means if a question wants you to calculate the frequency you know your final answer should be in heads okay it doesn't really matter if they are saying the frequency of the listener or the source but for the fact that a question set a frequency then your final answer should be in heads otherwise if it's a velocity ladies and gentlemen if it's a velocity then your answer should be in meters per second okay very much important ladies and gentlemen in meters per second so that means on this formula, ladies and gentlemen you only have two quantities or two types of quantities which is a the velocity or speed and frequency.

Okay so it's either you calculate the velocity or you calculate the frequency ladies and gentlemen please do not be confused by this information so what matters the most is the type of that particular frequency that you'll be calculating is it the frequency of the listener is it the frequency of the source is it the velocity of the listener or is it the velocity of the speed guys guys guys guys guys it's not only the velocity of the listener the velocity of the source frequency of the listener or frequency of the source that the examiner might want you to calculate very very much important ladies and gentlemen they can also want you to calculate the velocity of a you know the speed of sound in the air okay very very much important that you notice that the speed of the sound in the a ladies and gentlemen, you know it's measured in meters per second.

Why it's because it's a speed it's a velocity okay so guys let's now quickly uh sort out this question so i'm sure ladies and gentlemen some of you are done already with this question i know you already done i've actually delayed a you know quickly finishing with this question so that i give you a chance to try and solve this question because i know some of you ladies and gentlemen um you know exactly how to solve this type of questions but you are not confident until someone you trust a solve that particular question so ladies and gentlemen that's what i'm going to quickly do now so let's substitute so we've got f of the listener this is what the question wants us to calculate okay.

And i'm well aware ladies and gentlemen that your confusion only comes on that part over there okay but not many of you are confused when it comes to that part okay so this is equals to ladies and gentlemen in brackets you know i like substituting in brackets because you'll never go wrong what is the velocity of the speed in the air it's 340 meters per second so when i substitute it to the formula there's no need to write the unis okay so obviously this is the value that i just substituted ladies and gentlemen then here comes the question is it a plus or is it a minus a very interesting um question.

Ladies and gentlemen is it a plus or is it a minus ladies and gentlemen because the velocity of the listener is equals to zero whether you assume a sign over there to be a blast or a minus guys i'm going to give you a mark so um when we mark for your paper ladies and gentlemen especially with this type of questions if you assumed the sign for the listener to be a positive or otherwise if you assumed it to be negative for the fact that you know that the velocity of the listeners equals to zero either you choose to write a plus or a minus over there we are going to give you a mark.

Ladies and gentlemen because one thing for sure um over there guys over there and you won't just leave it blank but you should write a sign but remember guys between these two signs there's always a suitable sign a you know matching 100 with that scenario over there okay so uh guys if i were you i would use a positive sign why it's because the question says um you know a train is approaching um a train it's approaching the listener okay so even though ladies and gentlemen this the listener is stationary at that point okay but because there's a movement there's a movement a towards okay because there's a movement towards.

Ladies and gentlemen um it's more like somehow these two are approaching with each other okay if for a split second i can open my eyes and i notice there's a train at that spot and again there's a train at that spot then i quickly close my eyes and after say three seconds i open my eyes and i noticed now these two things are closer to each other ladies and gentlemen what am i thinking in my mind i know this and a you know there's a movement where something between these two is approaching okay so it's more like they are approaching with each other unlike if it's moving away okay if it's moving away ladies and gentlemen if for a split second i open my eyes and i notice uh these two in this position i close my eyes for 30 seconds then i open and i realize that train is somewhere there then i'm aware that okay these things they are moving away from each other so if they are moving away from each other i would use a negative sign over there.

If they are approaching with each other i would use a positive sign over there this information that i'm explaining is based on the fact that you've got a velocity of the listener being zero okay otherwise if it's not zero i might still at some point apply this information that i've provided okayso ladies and gentlemen i'm just trying to indicate to you that a for someone who who wrote a positive sign there or a negative sign it won't make any difference to the final answer or it won't negatively impact the final answer because 340 minus zero is still 340 340 plus zero is still 340 okay so ladies and gentlemen let's now substitute this part at the bottom so obviously i've just explained that v it doesn't change it remains as it is okay so now ladies and gentlemen excuse me so we need to choose between positive and negative sorry and negative okay so based on that information that i've explained to you.