Sound travels through air at approximately 330 metres per second. If the sound of thunder is heard 10 seconds after the flash of lightning, what is the approximate distance in kilometres of the thunder cloud?

Introduction / Context:

This question connects a simple time, speed and distance relationship to a real life phenomenon. When we see lightning and hear thunder after a delay, the time difference allows us to estimate how far away the thunder cloud is, because light travels almost instantaneously compared to sound. The problem gives the speed of sound and the time delay and asks for the distance of the cloud in kilometres.

Given Data / Assumptions:

• Speed of sound in air = 330 metres per second.
• Time delay between flash and thunder = 10 seconds.
• Speed is assumed constant throughout the travel of the sound.
• We neglect the time taken by light to reach us because it is extremely small compared to sound.
• We must report distance in kilometres.

Concept / Approach:

We use the basic formula distance = speed * time. First we compute the distance in metres by multiplying speed and time. Then we convert this distance into kilometres by dividing by 1000, because one kilometre equals 1000 metres. The result gives the approximate distance of the thunder cloud from the observer. This type of problem often appears in physics based aptitude tests and helps build comfort with unit conversions.

Step-by-Step Solution:

Verification / Alternative check:

As a quick mental check, if the delay were 3 seconds, the distance would be roughly 1 kilometre because 330 * 3 = 990 metres which is close to 1 km. For 10 seconds, we therefore expect a little more than 3 km. Our calculated value of 3.3 km fits this reasoning perfectly, reinforcing confidence in the numerical result.

Why Other Options Are Wrong:

Option 0.33 km would correspond to a distance of only 330 metres, which would require a delay of about 1 second, not 10 seconds. Option 33 km and 33.3 km are ten times larger than the correct distance and would require a delay of roughly 100 seconds at the given speed. They do not match the provided 10 second delay. Only 3.3 km is consistent with distance = 330 * 10 metres converted to kilometres.

Common Pitfalls:

Common mistakes include forgetting to convert metres into kilometres or misplacing the decimal point when dividing by 1000. Some learners also mistakenly multiply 330 by 100 instead of 10, or misread the speed as kilometres per hour. Always pay attention to the units given and perform conversions step by step to avoid errors.

Final Answer:

The thunder cloud is approximately 3.3 kilometres away from the observer.