Prelims 2026 · CSAT / Quantitative Aptitude · Question 41
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.<br/>
Answer
4:58:42 PM
Let the distance of the explosion spot from the camp be d metres. The second drone starts at 5:02 PM and its picture is received at 5:05 PM, so its travel time is 3 minutes = 180 s. Hence d = 30 × 180 = 5400 m. Sound takes 5400/300 = 18 s to reach the camp. The first drone then takes 5400/30 = 180 s to reach the spot. So the first picture is received 18 + 180 = 198 s = 3 min 18 s after the explosion. Therefore, explosion time = 5:02:00 PM − 3:18 = 4:58:42 PM.