Can anyone just check my answers and tell me if correct or not. If I’m incorrect, please tell me the correct answers...
On a windless day, train A is traveling down a grade at 50 m/s and passes train B, which is moving up the grade at half that speed. After the trains pass, train A blows it’s 300 Hz whistle. What frequency is heard by a passenger on train B.
312 Hz
435 Hz
243 Hz(my choice)
186 Hz
A police officer parked at the curb turns on his lights and siren, waits for traffic to clear, then pulls out and heads down the street. For an observer down the street, which is true?
The frequency of the siren is higher and the wavelength is shorter than it was at first.
The wavelength of the siren is shorter than it was at first, but the frequency is the same(my choice)
The wavelength of the siren is shorter and the frequency is lower than it was at first.
The frequency of the siren is higher than it was at first, but the wavelength is the same.
first is correct, second rethink. They are approaching, freq is higher.
Anyone help?
Given:
Va = 50 m/s.
Vb = 25 m/s.
Fp = (Vs-Vb)/(Vs+Va) * Fa.
Fp = (343-25)/(343+50) * 300 = 242.75 Hz. = Freq. heard by passenger.
Correct.
2. Answer is A.
To check if your answers are correct, let's analyze each question one by one:
1. On a windless day, train A is traveling down a grade at 50 m/s and passes train B, which is moving up the grade at half that speed. After the trains pass, train A blows its 300 Hz whistle. What frequency is heard by a passenger on train B?
To solve this, we need to consider the Doppler effect. When two objects are moving relative to each other, the frequency of the sound waves emitted by one object will be perceived differently by the other object. In this case, train B is moving towards train A.
The formula for the Doppler effect is:
f' = f * (v + vr) / (v + vs)
Where:
f' is the observed frequency,
f is the emitted frequency,
v is the speed of sound,
vr is the velocity of the receiver (train B in this case), and
vs is the velocity of the source (train A in this case).
Substituting the given values, we have:
f' = 300 Hz * (340 m/s + 0 m/s) / (340 m/s + 25 m/s)
f' = 300 Hz * (340 / 365)
f' ≈ 279 Hz
Therefore, the correct answer is not among the options you provided. The correct answer is around 279 Hz, which is not given as an option.
2. A police officer parked at the curb turns on his lights and siren, waits for traffic to clear, then pulls out and heads down the street. For an observer down the street, which is true?
When a source of sound (in this case, the police car's siren) is in motion, the frequency and wavelength of the sound waves change for an observer relative to the source. Since the police car is moving towards the observer, the frequency will increase, but the wavelength will decrease.
Therefore, for the observer down the street, this means the frequency of the siren is higher than it was at first, but the wavelength is shorter than it was at first. So, the correct answer is: "The frequency of the siren is higher than it was at first, but the wavelength is the same." This matches your choice.
Hope this explanation helps you understand the concepts behind these questions!