A person standing in front of a cliff fires a gun and hears its echo after 3s. If the speed of sound in air is $336 \mathrm{~ms}-1$. After moving a certain distance from the cliff he fires the gun again and this time the echo is heard 1.5 s later than the first. Calculate distance moved by the person.
Explanation
Let's assume the distance moved by the person is x. When the person is at the cliff, the time taken for the sound to reach the person and come back is 3s. When the person moves a distance x, the time taken for the sound to reach the person and come back is 3s + 1.5s = 4.5s. Since the speed of sound is constant, the distance traveled by the sound in 4.5s is 4.5 times the speed of sound. The distance traveled by the sound in 3s is 3 times the speed of sound. Therefore, the distance moved by the person is the difference between the two distances, which is (4.5 - 3) times the speed of sound. So, the correct option is D.
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