UPSC Prelims 2026 · CSAT Paper 2 · Set DMathematicsQ 21 / 80

UPSC Prelims 2026 CSAT Paper 2 — Question 21

Question

An explosion takes place at a certain distance from an army camp. As soon as the sensor in the camp receives the sound of the explosion, a drone starts flying towards the spot of explosion. The drone clicks a picture from the spot and the camp receives it at the same time. Immediately another drone starts flying to the spot and it also sends a picture as soon as it reaches the spot. The two pictures were received at 5:02 PM and 5:05 PM, respectively. If the speed of the drones is 30 m/s, at what time did the explosion take place? Assume that the speed of sound is 300 m/s.

(a)4:59:00 PM
(b)4:59:02 PM
(c)4:58:42 PM
(d)4:56:32 PM

UnlockIAS answer: (c)4:58:42 PM

Solution

The second drone's flight takes 5:05 − 5:02 = 180 s at 30 m/s, so the distance D = 5400 m. The explosion occurred at 5:02 − (D/300 + D/30) = 5:02 − (18 + 180) s = 5:02 − 198 s = 4:58:42 PM.

UnlockIAS expert key, prepared 24 May 2026 and cross-verified by re-deriving the answer — this is our key, not the official UPSC provisional key (awaited).

Section

Mathematics

Topic Reference

Numeracy — Speed, time and distance

Official UPSC key still awaited

UPSC has announced (PIB Release 2262441, 18 May 2026) that the provisional answer key for CSE Prelims 2026 will be released “soon after Exam”. Until then, use the CSAT score calculator for your qualifying-status estimate, and join the per-question discussion below.

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Official Notification

PIB Release 2262441

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