Question
A radar used to detect the presence of aircraft receives a pulse that has reflected off an object 6×105 s6 \times 10^{-5} \textrm{ s} after it was transmitted. What is the distance from the radar station to the reflecting object?
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Final Answer

9 km9 \textrm{ km}

Solution video

OpenStax College Physics, Chapter 24, Problem 13 (Problems & Exercises)

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Video Transcript
This is College Physics Answers with Shaun Dychko. This radar emits a pulse of light and that's reflected-off this aircraft and returns to the radar sometime later. And so we want to find how far is the aircraft from the radar given a certain amount of time it takes to do this round trip; while doing the round trip means doing the trip twice. So covering this distance d twice and so we have 2 times the distance between the aircraft in the radar equals the speed of this wave, which is the speed of light c multiplied by the total time it takes to do the round trip. And so we'll divide both sides by 2 to solve for d. And we get d then is the speed of light 3 times 10 to the 8 meters per second multiplied by the time between emission and detection of the reflected pulse, which is 6 times 10 to the minus 5 seconds and divide that by 2 to get a distance of 9 kilometers and only one significant figure is appropriate here because our time measurement is one significant figure.