Question

Two identical speakers are positioned the same distagce from a guitarist. The intensity of sound delivered by each operating speaker at the guitarist's location is 1.2x10 W/m. A Determine the sound loul hi

A.Determine the sound level heard by the guitarist when one speaker is operating .Units dB

B.Determine the sound level heard by the guitanist when both speakers are operating .Units dB

A. The frequency of the signal as determined by the motor vehicle .Units MHz

B.The frequency determined by the radar speed gun for the signal reflected back to it by the motor vehicle .Units :Hz

Answer 1

1) A. We use the sound intensity formula

$\beta =10\log \left ( \frac{I}{I_{0}} \right )$

$\beta =10\log \left ( \frac{1.2\times 10^{-7}\frac{W}{m^{2}}}{10^{-12}\frac{W}{m^{2}}} \right )=50.79dB$

B. When both speakers are operating

$\beta =10\log \left ( \frac{2.4\times 10^{-7}\frac{W}{m^{2}}}{10^{-12}\frac{W}{m^{2}}} \right )=53.8dB$

2. A. According to the doppler effect equation, the frequency perceived by and observer moving towards the source is

${f}'=f\left ( \frac{V+V_{o}}{V} \right )$

Where V is the velocity of sound = 343 m/s = 1234.8 km/h

${f}'=9MHz\times \left ( \frac{1234.8\frac{km}{h}+70\frac{km}{h}}{1234.8\frac{km}{h}} \right )=9.5MHz$

B. Now the source (the reflected signal of the calculated frequency) is moving thowards an stationary observer and the equation is

${f}'=f\left ( \frac{V}{V-V_{s}} \right )$

${f}'=9.51MHz\times \left ( \frac{1234.8\frac{km}{h}}{1234.8\frac{km}{h}-70\frac{km}{h}} \right )=10.1MHz$