It Is Possible to Hear an Approaching Train Before You

question 7

Multiple Choice

It is possible to hear an approaching train before you can see it by listening to the sound wave through the track. If the elastic modulus is 2.0 × 10¹¹ N/m² and the density of steel is 7.8 × 10³ kg/m³, approximately how many times faster is the speed of sound in the track than in air? (v_air ≈ 340 m/s.)

• A) 20
• B) 5
• C) 10
• D) 15
• E) 25

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