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# Two children are at opposite ends of an aluminium rod. One strikes the end of the rod with a stone. Find the ratio of times taken by the sound wave in the air and in aluminium to reach the second child.

p>Consider the length of aluminium rod = d

Speed of sound wave at 25° C in aluminium, $$V_{Al} = 6420 m/s$$

Time taken to reach other end

$$T_Al = \frac{d}{V_{Al} }= \frac{d}{6420}$$

Speed of sound in air, $$V_{air} = 346 m/s$$

Time taken by sound to each other end,

$$T_{air} = \frac{d}{V_{air} } = \frac{d}{346}$$

$$\therefore$$ the ratio of time taken by sound in aluminium and air,

= $$\frac{T_{air}}{t_{Al}} = \frac{6420}{346} = 18.55$$