Here is the question that I am having troublewith. An automobile is approaching you at a speed of 90 Km/h andsounding its horn. The fundamental frequency of the hornsounds to you like 268 Hz. If the real fundamental frequencyof the horn is 248 Hz, what is the speed of sound? I was having trouble understanding how to work out the formulawhen I was missing the very thing they were asking for. Iknow it is probably really easy, but I can't seem to figure itout. Thanks. Here is the question that I am having troublewith. An automobile is approaching you at a speed of 90 Km/h andsounding its horn. The fundamental frequency of the hornsounds to you like 268 Hz. If the real fundamental frequencyof the horn is 248 Hz, what is the speed of sound? I was having trouble understanding how to work out the formulawhen I was missing the very thing they were asking for. Iknow it is probably really easy, but I can't seem to figure itout. Thanks.
Explanation / Answer
when the source is approaching a stationary observer theapparent frequency is n' = (n/1 - (vs/v)) solving the above equation for v v = [vs/1 - (n/n')] vs= 90 km/h = 90 * (1000/3600) m/s = 90 * (5/18)m/s = 25 m/s n = 248 Hz n' = 268 Hz