To determine which boy would be able to hear a rock falling off a cliff one kilometer away, we should consider how sound travels through different materials according to the data provided.
Sound travels fastest in solids (like rock) and then in liquids (like water), while it travels slowest in gases (like air).
Here are the velocities for each medium:
- Air: 344 m/s
- Water: 1,437 m/s
- Rock: 3,000 m/s
1 kilometer (1,000 meters) is the distance the sound must travel.
- A boy swimming in the water: Sound would travel at 1,437 m/s. Time to reach him = 1,000 m / 1,437 m/s ≈ 0.696 seconds.
- A boy sitting in a tree with his ear to the bark: Sound would travel through the tree (which is a solid and likely has a speed closer to that of rock). He would hear it fastest this way.
- A boy sitting on the grass: Sound would travel through the air at 344 m/s. Time to reach him = 1,000 m / 344 m/s ≈ 2.91 seconds.
- A boy lying down with his ear to the ground: Sound would travel through the ground, which would also be fast but not as fast as rock.
Given that the tree (assuming a solid structure) will transmit sound faster than air but slower than rock, he would most likely hear it quickly.
Based on this analysis, the boy sitting in a tree with his ear to the bark would have the best chance of hearing the rock falling quickest, as sound would travel through the tree (a solid) more effectively than through other options involving air.
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