Question

In: Physics

A bicyclist is pedaling down a road at 8 m/sec. A car approaches him from behind....

A bicyclist is pedaling down a road at 8 m/sec. A car approaches him from behind. When the car is preparing to pass he sounds his horn. At first the bicyclist hears a frequency of 520 HZ but the sound appears to drop in frequency to 470 HZ after the car passes.

a) How fast is the car moving? (v sound = 340 m/sec)(answer to nearest whole number)

b) what is the actual frequency of the horn (don't assume it is the average of the 2 perceived frequencies)

Solutions

Expert Solution

frequency observed by an moving observer, when the source approaches the observer from behind is : [ = frequency observed, = original frequency, v = speed of sound, vs = speed of source, vo = speed of observer]

frequency observed by an moving observer, when the source moves away from the observer moving in the same direction is : [ = frequency observed, = original frequency, v = speed of sound, vs = speed of source, vo = speed of observer]

given : observed frequency in the first case = 520 Hz

observed frequency in the second case = 470 Hz

v = speed of sound = 340 m/s

vo = spedd of bicyclist = 8 m/s

vs = speed of car = ?

= actual frequency = ?

first case in the problem :

-------(i)

second case :

------(ii)

a) dividing the equation (i) and (ii) :

=> vs = 25 m/s [answer]

b) putting the value of vs in, say equation (i) :

=> = 493.4 Hz [answer]

genius_generous answered 1 year ago

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