# Physics

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.

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1. Anyone help?

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2. first is correct, second rethink. They are approaching, freq is higher.

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3. 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.

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