en Physics 113-Sumer 2018 Problem 1: A train is moving past a crossing where car

Question

en Physics 113-Sumer 2018 Problem 1: A train is moving past a crossing where cars are waiting for it to pass. While waiting, the driver of the lead car becomes sleepy and rests his head on the steering wheel, unintentionally activating the car's horn. A passenger in the back of the train hears the horn's sound at a frequency of 439 Hz and a passenger in the front hears it at 413 Hz. Find the train's speed and the horn's frequency, assuming the sound travels along the tracks Take the speed of sound to be 343 m/s. Problem 2: Two cars are on the same straight road. Car A moves east at 55 mph and sounds its horn at 625 Hz. Rank from highest to lowest the frequency observed by Car B's driver in each of the following cases. (Use the following as necessary: a, b, c, and d. U "or""symbols. Do not include any parentheses around the letters or symbols. Let "behind" mean car B is west of car A, and "in front of" mean car B is east of car A) (a) Car B is moving east at 70 mph and is behind car A. (b) Car B is moving east at 70 mph and is in front of car A. se only 416Sq 5 4342.81 (d) Car B is moving west at 70 mph and is in front of car A. 343+ 343 Vo 33 313-0

Explanation / Answer

1)

let the speed of the train is v

and the frequency of horn is f0

for the passenger at the back of the train

439 = f0 * (343 + v)/(343)

Now, for the passenger at the front of the train

413 = f0 * (343 - v)/(343)

solving for f0 and v

v = 10.5 m/s

f0 = 426 Hz

the speed of the train is 10.5 m/s

the frequency of the car horn is 426 Hz

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