Question

A disused railway line has a length of 300 m. A man puts his ear against one end of the rail and another man hits the other end with a metal hammer, as shown in figure.

(a) (i) State an approximate value for the speed of sound in air. (ii) Sound travels at 5000 m/s in steel. Calculate the time it takes for the sound to travel along the rail. (b) The man with his ear to the railway line actually hears two sounds from the hammer, separated by a short interval. Explain why he hears two sounds.

Sound CBSE Class 9

CBSE, Class 9, Exam Idea, Science

August 7, 2024

Answer

(a) (i) The approximate value for the speed of sound in air is 344 m/s

(ii) Distance = 300 m, Speed = 5000 m/s

∴ Time taken = ${Distance \over Speed}$ = ${300\over5000}$ = 0.06 s

(b) As we know, the speed of sound is different in different materials. Sound travels about 15 times faster in steel than in air. The man hears two sounds one through air and other through railway line made of steel.

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