A learner in a car, moving at a constant speed of 10 m s⁻¹ along a straight horizontal road, records the frequency of sound emitted by a distant stationary source. The learner then repeats the recording of the frequency of the sound when the car travels at a new constant speed of 20 m s⁻¹. The graph below, not drawn to scale, is obtained from the results. **Graph Reference**: See the frequency vs. speed graph provided. 6.1 State the Doppler effect. 6.2 Use the graph to answer the following questions. 6.2.1 Write down the frequency of the sound emitted by the stationary source. 6.2.2 In which direction is the car moving relative to the source? Choose from TOWARDS or AWAY. 6.2.3 Calculate the speed of sound in air.

NSC Physical Sciences Doppler Effect: A learner in a car, moving at a

A learner in a car, moving at a constant speed of 10 m s⁻¹ along a straight horizontal road, records the frequency of sound emitted by a distant stationary source - NSC Physical Sciences - Question 6 - 2021 - Paper 1

Question 6

A learner in a car, moving at a constant speed of 10 m s⁻¹ along a straight horizontal road, records the frequency of sound emitted by a distant stationary source. ... show full transcript

Worked Solution & Example Answer:A learner in a car, moving at a constant speed of 10 m s⁻¹ along a straight horizontal road, records the frequency of sound emitted by a distant stationary source - NSC Physical Sciences - Question 6 - 2021 - Paper 1

Step 1

State the Doppler effect.

96%

114 rated

Answer

The Doppler effect refers to the change in frequency (or pitch) of a sound observed by a listener moving relative to a sound source. This effect occurs due to the motion of either the source, the observer, or both. If the source and observer are moving closer together, the observed frequency increases. Conversely, if they are moving apart, the observed frequency decreases.

Step 2

Write down the frequency of the sound emitted by the stationary source.

99%

104 rated

Answer

The frequency of the sound emitted by the stationary source is 700 Hz. This can be deduced from the graph, where the frequency is represented on the y-axis.

Step 3

In which direction is the car moving relative to the source? Choose from TOWARDS or AWAY.

96%

101 rated

Answer

The car is moving AWAY from the source. This conclusion is based on the observation that the recorded frequency decreases as the speed of the car increases.

Step 4

Calculate the speed of sound in air.

98%

120 rated

Answer

To calculate the speed of sound, we can use the formula for the Doppler effect:

$f_t = f_s \frac{v \pm v_l}{v}$

Where:

$f_t$ = observed frequency,
$f_s$ = source frequency (700 Hz),
$v_l$ = velocity of the listener (speed of the car), and
$v$ = speed of sound in air.

Using the graph for frequency recorded (for example, 679.1 Hz at 10 m/s):

$679.1 = 700 \frac{v - 10}{v}$

Rearranging gives:

$v = \frac{679.1 \cdot v + 7000 - 700 \cdot 10}{679.1}$

Calculating with values, we find: $v \approx 334.93 \text{ m s}^{-1}$

Therefore, the speed of sound in air is approximately 334.93 m s⁻¹.

A learner in a car, moving at a constant speed of 10 m s⁻¹ along a straight horizontal road, records the frequency of sound emitted by a distant stationary source - NSC Physical Sciences - Question 6 - 2021 - Paper 1

Worked Solution & Example Answer:A learner in a car, moving at a constant speed of 10 m s⁻¹ along a straight horizontal road, records the frequency of sound emitted by a distant stationary source - NSC Physical Sciences - Question 6 - 2021 - Paper 1

State the Doppler effect.

Write down the frequency of the sound emitted by the stationary source.

In which direction is the car moving relative to the source? Choose from TOWARDS or AWAY.

Calculate the speed of sound in air.

Join the NSC students using SimpleStudy...