A man covers 1/4 of his total journey at 20 km/h and the remaining 3/4 at 40 km/h. Find his average speed for the entire journey. MCQ with Answer and Explanation
A man covers 1/4 of his total journey at 20 km/h and the remaining 3/4 at 40 km/h. Find his average speed for the entire journey.
A. 36.0 km/h
B. 30.5 km/h
C. 34.2 km/h
D. 32.0 km/h
Answer: Option D
Solution (By JKSSB Mock Tests)
Let total distance be 80 km. First part = 20 km; Time = 20 / 20 = 1 hour. Remaining part = 60 km; Time = 60 / 40 = 1.5 hours. Total distance = 80 km, Total time = 2.5 hours. Average speed = 80 / 2.5 = 32 km/h.
Two cars leave a location simultaneously at a right angle to each other. Their speeds are 36 km/h and 48 km/h respectively. Find the direct distance between them after 15 minutes.
Explanation:
Time = 15 minutes = 0.25 hours. Distance covered by first car = 36 * 0.25 = 9 km. Distance covered by second car = 48 * 0.25 = 12 km. Since they travel at right angles, distance between them = sqrt(9^2 + 12^2) = sqrt(81 + 144) = sqrt(225) = 15 km.
Two trains 140 meters and 160 meters long are running at the speeds of 60 km/h and 40 km/h respectively in opposite directions on parallel tracks. What is the time taken by them to cross each other completely?
Two cars start from the same spot and travel along perpendicular roads. One travels at 15 km/h and the other at 20 km/h. Find the distance between them after 2 hours.
Explanation:
In 2 hours, the first car travels 30 km and the second car travels 40 km. Direct distance = sqrt(30^2 + 40^2) = sqrt(900 + 1600) = sqrt(2500) = 50 km.
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