A siren on an ambulance emits sound at a constant frequency of 750 Hz - Scottish Highers Physics - Question 8 - 2015

The frequency observed can be calculated using the formula:

f' = rac{f (v + v_0)}{v - v_s}

Where:

• $f'$ is the observed frequency,
• $f$ is the source frequency (750 Hz),
• $v$ is the speed of sound in air (340 m/s),
• $v_0$ is the speed of the observer (0 m/s, since the observer is stationary),
• $v_s$ is the speed of the source (25.0 m/s, since the ambulance is moving towards the observer).

Substituting these values, we get:

f' = rac{750 ext{ Hz} (340 ext{ m/s} + 0 ext{ m/s})}{340 ext{ m/s} - 25.0 ext{ m/s}}

Calculating it:

• The denominator becomes: 340 - 25 = 315 m/s.

Thus,

f' = rac{750 imes 340}{315}

Now, performing the calculation:

ightarrow 805.56 ext{ Hz}$$ Rounding to the nearest whole number, the frequency heard by the observer is approximately 806 Hz.