Two trains, A and B

PHYSICS · Single correct · AP · Physics 2: Algebra-based · Waves Sound and Physical Optics · Waves Sound and Physical Optics

Problem

Two trains, A and B, move on parallel tracks towards a stationary observer O. Train A’s whistle has a frequency of

500\,\text{Hz}

and approaches O with a speed of

15\,\text{m\,s}^{-1}

. Train B’s whistle has a frequency of

480\,\text{Hz}

. The observer hears

5

beats per second and notes that the pitch coming from train B is lower than that from train A. Calculate the speed of train B. (Speed of sound in air

=340\,\text{m\,s}^{-1}

.) (a)

26\,\text{m\,s}^{-1}

(b)

25\,\text{m\,s}^{-1}

(c)

31\,\text{m\,s}^{-1}

(d)

24\,\text{m\,s}^{-1}