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 × 10^11 N/m2 and the density of steel is 7.8 × 10^3 kg/m3, approximately how many times faster is the speed of sound in the track than in air? (vair ? 340 m/s.)
a. 20
b. 5
c. 10
d. 15
e. 25
d
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