Question

The children are at opposite ends of metal rod. One strikes the end of the rod with big pebble. Find the ratio of time taken by the sound waves in air and in the metal to reach it second child. (Speed in rod = 6420 m/s).

• A. 221.3
• B. 18.55
• C. 22.13
• D. 185.5

Answer 1

The correct option is B 18.55

Let the length of road is $l$ .

time taken by sound wave to reach to other child through metal rod ,

time=distance/speed ,

$t_m=l/v_m=\left(l/6420\right)$ second , (given ,$v_m=6420m/s$) ,

time taken by sound wave to reach to other child through air ,

time=distance/speed ,

$t_a=l/v_a=\left(l/340\right)$ second , (we have ,$v_a=340m/s$) ,

dividing $t_a$ by $t_m$ , we get

$t_a/t_m=6420/340=18.88$ ,

or $t_a:t_m=18.88:1$