किसी सैन्य शिविर से कुछ दूरी पर एक विस्फोट होता है। शिविर में लगा संवेदक (सेंसर) जैसे ही विस्फोट की ध्वनि को ग्रहण करता है, एक ड्रोन विस्फोट स्थल की ओर उड़ान भरता है। ड्रोन उस स्थल की तस्वीर लेता है और शिविर को उसी क्षण वह तस्वीर मिल जाती है। तत्काल एक अन्य ड्रोन उस स्थल के लिए उड़ान भरता है और वह भी उस स्थल पर पहुँचते ही तस्वीर भेजता है। ये दो तस्वीरें क्रमशः 5:02 PM और 5:05 PM पर मिली थीं। यदि ड्रोनों की चाल 30 m/s है, तो विस्फोट कितने बजे हुआ था? मान लीजिए कि ध्वनि की चाल 300 m/s है।
Read this question in English
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
उत्तर और व्याख्या · explanation in English
Answer: (c) 4:58:42 PM
The second drone's one-way trip takes the 3 minutes between the two pictures, so the spot is 180 × 30 = 5400 m away. The first drone left 3 minutes before 5:02, and the sound had taken 5400 ÷ 300 = 18 s to arrive, so the explosion was 3 min 18 s before 5:02 PM.
- The second drone starts at 5:02 PM and its picture arrives at 5:05 PM, so one trip takes 180 s.
- Distance = 30 m/s × 180 s = 5400 m.
- The first drone also needed 180 s, so it left the camp at 4:59:00 PM — the moment the sound arrived.
- Sound took 5400 ÷ 300 = 18 s, so the explosion happened at 4:59:00 − 18 s = 4:58:42 PM.
- Check: 4:58:42 + 18 s + 180 s = 5:02:00 PM.
Remember · Work backwards on a timeline: find the distance from the cleanest interval, then subtract each leg's travel time.
Question and answer: UPSC's provisional GS Paper II (2026, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). ·