For an outdoor lab experiment a car has a loud device attached to the roof. This device emits beeps with a pitch of 400 Hz. The device is set to constantly emit short beeps a rate of twice every second. The car drives at 25 m/s (About 55 mph) on a level track towards a student with a frequency meter. Which of the following correctly describes both the pitch of the individual beeps measured by the student and the rate that the student hears the beeps?
A. Pitch of each beep :The student measures each beeps pitch as lower than 400 Hz
Rate of Beeps:The student hears exactly 2 beeps per second
B. Pitch of each beep: The student measures each beeps pitch as higher than 400 Hz
Rate of Beeps : The student hears more than 2 beeps per second
C. Pitch of Each beep: the student measures each beeps pitch as exactly 400 Hz
Rate: The students hears more than 2 beeps per sec
D. The student measures each beeps pitch as higher than 400
Rate of beeps: student hears exactly 2 beeps per sec
The answer is B but can someone explain why that is true? I got this wrong on my test but I am doing corrections
The correct answer is B. Here's the explanation:
When a source of sound, such as the loud device attached to the car, moves towards an observer, the frequency of the sound waves (or the pitch) appears higher than its actual frequency. This phenomenon is called the Doppler effect.
In this case, the car has a loud device emitting beeps at a constant frequency of 400 Hz. As the car is driving towards the student, the sound waves are compressed, causing an increase in perceived pitch.
Additionally, the car emits two beeps every second. However, since the car is moving towards the student, the sound waves are being "compressed" in the direction of their motion. As a result, the rate at which the student hears the beeps will be higher than the emission rate of the beeps. This means the student hears more than two beeps per second.
Therefore, the correct answer is B: The student measures each beep's pitch as higher than 400 Hz, and the student hears more than 2 beeps per second.
To determine the correct answer, we need to consider the concepts of the Doppler effect and how it applies to this situation.
The Doppler effect is the change in frequency or pitch of a sound wave for an observer moving relative to the source of the sound. When the source of sound and the observer are moving towards each other, the frequency or pitch appears to increase. On the other hand, when they are moving away from each other, the frequency or pitch appears to decrease.
In this scenario, the car is moving towards the student with a constant velocity of 25 m/s. The device on the car emits beeps at a constant pitch of 400 Hz.
Taking this information into account, we can analyze the answer options:
A. Pitch of each beep: The student measures each beep's pitch as lower than 400 Hz
Rate of beeps: The student hears exactly 2 beeps per second
This option is incorrect because, according to the Doppler effect, when the car and the student are approaching each other, the pitch of each beep should be higher, not lower.
C. Pitch of Each beep: the student measures each beep's pitch as exactly 400 Hz
Rate: The student hears more than 2 beeps per second
This option is also incorrect because, as the car and the student are approaching, the pitch should be higher than the actual pitch of 400 Hz.
D. The student measures each beep's pitch as higher than 400
Rate of beeps: the student hears exactly 2 beeps per second
This option is incorrect because, as the car and the student are approaching each other, the pitch should be higher, not lower.
Therefore, the correct answer is B.
B. Pitch of each beep: The student measures each beep's pitch as higher than 400 Hz
Rate of Beeps: The student hears more than 2 beeps per second
This option is correct because, as the car and the student are approaching each other, the pitch of each beep will be higher due to the Doppler effect. Additionally, since the car emits beeps at a rate of twice every second, the student will hear more than 2 beeps per second as the car approaches.
By understanding the concept of the Doppler effect and its application in this scenario, you can correctly determine the answer.