The table displays the velocity of sound in various materials.
Based on the data presented in the table, which of the following boys would be able to hear a rock falling off a cliff one kilometer away?
a. a boy sitting on the grass
b. a boy swimming in the water
c. a boy lying down with his ear to the ground
d. a boy sitting in a tree with his ear to the bark
The answer is c. a boy lying down with his ear to the ground.
This is because sound travels fastest through solids compared to other materials. The velocity of sound in solid rock is 6000 m/s, while the velocity of sound in air is only about 343 m/s. Therefore, if the boy has his ear directly on the ground, he would be able to hear the sound of the rock falling off the cliff before anyone else in the given options.