A man is standing near a three blade wind turbine he counted the rotations that

Question

A man is standing near a three blade wind turbine he counted the rotations that it does, he counted fifteen complete rotations per minute. Each time one of the blades passed the tower he heard a "whoosh" sound What would be the frequency of this sound be if he was driving away from the turbine at 40 km/h into a 10 km/h headwind? give your answer in Hz. A diagram which includes the source of the sound. Your position as the observer and the direction of the wind should be included in your answer. The sound of the wind turbine reflects off a hard rock face in front of you as you drive around the headland. What is the frequency of the reflected noise that you hear from the turbine?

Explanation / Answer

Answer:-

Given Data:-

Par-1 ) Calcualte the frequency.

we have to calcualate first a source frequency.

we have given a 15 rpm

we know that 1rpm = 1/60 Hz

so 15 rpm = 15 *1/60 Hz

fs = 0.25 Hz.

Listener velocity vL = 40 km/hour convert it in to m/s

So  vL = 11.11 m/sec

velocity of the source vs = 10 km/hour conver it in to the m/sec

vs = 2.77 m/s

we have to find the frequency listen by the listner. use a below formula.

fL = ( v -vL / v+vS ) *fs take a listner velocity is negative.   conisde the v =velocity of speed of the waves (speed of sound in air) = 340 m/s

fL = ( 340 -11.11/ 340+2.77 ) *0.25

fL = 0.95*0.25

fL = 0.239 Hz.   

Hence the frequency is 0.239 Hz.

Part-2)

Use a same formula to calcualte the frequency only use the listenr velocity as a positive.

fL = ( v +vL / v+vS ) *fs

fL = ( 340 +11.11/ 340+2.77 ) *0.25

fL = 1.02*0.25

fL =0.256 Hz.

Hence the frequency is 0.256 Hz.

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.