Lightning can be seen at the moment when it occurs. Paheli observes lightning in her area. She hears the sound $5 s$ after the observed lightning. How far is she from the place where lightning occurs? (Speed of sound = $330 m / s$ )

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66 m

1.65 km

165 km

16.5 km

answer is B.

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Detailed Solution

Lightning can be seen at the moment when it occurs. Paheli observes lightning in her area. She hears the sound

5 s

after the observed lightning. Paheli is

1.65 km

from the place where lightning occurs.
We know that time is

5 s

and speed of sound is

330 m / s

.
So,

distance = speed \times time

\Rightarrow distance = 330 \times 5

\Rightarrow distance = 1650 m

\Rightarrow distance = 1.65 km

Here, Paheli first sees the flash of lightning and then hears its sound. This is because the speed of light is very fast as compared to the speed of sound. Speed of sound changes with change in medium. The speed of sound also depends on the temperature of the medium. The speed of sound is higher at higher temperatures.

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