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Q134
(IAS/1999)
Science & Technology › Basic Science (Physics, Chemistry, Biology) › Quantitative aptitude topics
Answer Verified
The average speed of a train in the onward journey is 25% more than that of the return journey. The train halts for one hour on reaching the destination. The total time taken for the complete to and fro journey is 17 hours covering a distance of 800 km. The speed of the train in the onward journey is
Result
Your answer:
—
·
Correct:
D
Explanation
Apply the distance–speed–time relation (as illustrated in standard motion examples) [1]. Let the return speed be v km/h, so onward speed = 1.25v. One-way distance = 800/2 = 400 km. Time for onward = 400/(1.25v) = 320/v hours; time for return = 400/v hours. Including the 1-hour halt, total time: 320/v + 400/v + 1 = 17. Hence 720/v = 16, giving v = 45 km/h as the return speed. Onward speed = 1.25 × 45 = 56.25 km/h. This uses the standard uniform-motion treatment for trains and distances [2], so the correct choice is option 4 (56.25 km/h).
Sources
- [1] Science-Class VII . NCERT(Revised ed 2025) > Chapter 8: Measurement of Time and Motion > Let Us Enhance Our Learning > p. 119
- [2] Science-Class VII . NCERT(Revised ed 2025) > Chapter 8: Measurement of Time and Motion > 8.4 Uniform and Non-uniform Linear Motion > p. 117
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