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SSC CHSL Relative Speed

Study Material — 1 PYQs (2018–2018) · Concept Notes · Shortcuts

SSC CHSL Relative Speed is a frequently tested subtopic — 1 previous year questions from 2018–2018 papers are included below with concept notes, key rules and shortcut tricks.

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2018–2018
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10 Key Points
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Previous Year Questions

SSC CHSL Relative Speed — Past Exam Questions

1 questions from actual SSC CHSL papers · all shown free · click option to reveal solution

Exam Q 12018Previous Year Pattern

Two trains start simultaneously from stations A and B, which are 450 km apart. Train X travels from A towards B at 60 km/h, while Train Y travels from B towards A at 90 km/h. After how much time will they meet, and at what distance from station A?

Concept Notes

Relative Speed— Rules & Concept

Core ConceptRead this first — the foundation of the topic
Core Concept

When two objects move, their relative speed depends on their direction. If they move towards each other, speeds add up. If they move in the same direction, speeds subtract. Imagine two trains - one coming towards you at 60 kmph while you travel at 40 kmph.

The relative speed is 100 kmph

Key Rules

For objects moving towards each other: Relative Speed = Speed1 + Speed2. For objects moving in same direction: Relative Speed = |Speed1 - Speed2|. For objects moving in opposite directions: Relative Speed = Speed1 + Speed2.

Formula BlockMemorise — at least one formula appears in every paper
• When approaching: Relative Speed = S1 + S2
• When separating/same direction: Relative Speed = |S1 - S2|
• Time to meet = Total Distance / Relative Speed
• Time to cross = (L1 + L2) / Relative Speed (for trains)
Exam PatternsWhat examiners ask — read before attempting PYQs

SSC loves asking about trains crossing each other, people walking towards/away from each other, and boats in rivers. Questions often involve calculating meeting time, crossing time, or finding individual speeds when relative speed is given.

ShortcutsUse these to save 30–60 seconds per question

#1: For train problems, always add train lengths when calculating crossing time. The faster train needs to cover the combined length of both trains to completely cross.

Worked ExampleSolve this step-by-step before moving on
1
Step 1

Convert speeds to m/s: 54 kmph = 54 × 5/18 = 15 m/s, 36 kmph = 36 × 5/18 = 10 m/s

2
Step 2

Relative speed = 15 + 10 = 25 m/s (opposite directions)

3
Step 3

Combined length = 120 + 80 = 200m

4
Step 4

Time = Distance/Speed = 200/25 = 8 seconds Shortcut Trick #2: Speed conversion hack: kmph to m/s, multiply by 5/18. m/s to kmph, multiply by 18/5. Remember: 5/18 ≈ 0.278, 18/5 = 3.6 Worked Example 2: A man walks at 5 kmph. A car travels at 45 kmph in same direction. If car is initially 2 km behind, when will it catch up?

1
Step 1

Relative speed = 45 - 5 = 40 kmph (same direction, so subtract)

2
Step 2

Distance to cover = 2 km

3
Step 3

Time = Distance/Relative Speed = 2/40 = 0.05 hours = 3 minutes Shortcut Trick #3: For meeting point problems, use the ratio method. If two objects start from opposite ends with speeds S1 and S2, they meet at a point dividing the distance in ratio S1:S2. Most

Exam TrapsCommon mistakes students make — avoid these

Students forget to add lengths when trains cross each other. They only use train speeds but ignore that crossing means one train must travel its own length plus the other train's length. Always remember: crossing distance = sum of lengths, not just individual train length. Another frequent error is wrong direction calculation.

When objects move towards each other, always add speeds. When in same direction, always subtract. Never confuse these basic rules, as they form the foundation of every relative speed problem in SSC CGL.

Key Points to Remember

  • Relative speed = S1 + S2 when objects move towards each other
  • Relative speed = |S1 - S2| when objects move in same direction
  • For train crossing: Time = (L1 + L2) / Relative Speed
  • Speed conversion: kmph to m/s multiply by 5/18
  • Meeting time = Total distance / Relative speed
  • When trains cross, always add both train lengths to find distance
  • Objects starting from opposite ends meet at distance ratio S1:S2
  • In river problems: Downstream speed = Boat speed + River speed
  • Upstream speed = Boat speed - River speed
  • Relative speed is always positive, use absolute value for same direction

Exam-Specific Tips

  • Speed conversion factor from kmph to m/s is exactly 5/18
  • Speed conversion factor from m/s to kmph is exactly 18/5 or 3.6
  • When two trains cross each other, distance = sum of both train lengths
  • For circular track problems, relative speed determines lap completion time
  • Meeting point divides total distance in ratio of individual speeds
  • In boat problems, still water speed = (Downstream + Upstream)/2
  • River current speed = (Downstream - Upstream)/2
  • Two objects starting together separate at their relative speed rate
Practice MCQs

Relative Speed — Practice Questions

26graded MCQs · easy to hard · full solution & trap analysis · showing 20 of 26

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Practice 1easy

A cyclist and a runner start from the same point and move in the same direction. The cyclist travels at 24 km/h and the runner at 8 km/h. After how much time will the cyclist be 32 km ahead of the runner?

Practice 2easy

A boat travels downstream at 15 km/h and upstream at 9 km/h. What is the speed of the boat in still water?

Practice 3easy

Two cars start from the same location and travel in opposite directions. Car X travels at 50 km/h and Car Y travels at 70 km/h. How far apart will they be after 3 hours?

Practice 4easy

A person walks at 4 km/h. If he walks for 2.5 hours, how many metres does he cover?

Practice 5easy

Two trains are moving towards each other on parallel tracks. Train A travels at 60 km/h and Train B travels at 40 km/h. If they are initially 500 km apart, in how many hours will they meet?

Practice 6easy

A man cycles at 15 km/h and a woman cycles at 10 km/h in the same direction on the same road. If the woman starts 30 km ahead, how long will it take the man to catch up with the woman?

Practice 7easy

A boat travels upstream at 8 km/h and downstream at 12 km/h. What is the speed of the boat in still water?

Practice 8easy

Two runners start from the same point and run in opposite directions. Runner A runs at 12 km/h and Runner B runs at 8 km/h. After how many hours will they be 60 km apart?

Practice 9easy

A car travels 120 km in 2 hours. A motorcycle travels at a speed 25% faster than the car. How far will the motorcycle travel in 3 hours?

Practice 10easy

Two trains are moving towards each other on parallel tracks. Train A travels at 60 km/h and Train B travels at 40 km/h. If they are initially 200 km apart, how long will it take for them to meet?

Practice 11medium

A man cycles at 15 km/h and a woman cycles at 10 km/h in the same direction on the same road. If the man starts 20 km behind the woman, how long will it take for the man to catch up with the woman?

Practice 12medium

A boat travels upstream at 8 km/h and downstream at 12 km/h in a river. What is the speed of the boat in still water and the speed of the current?

Practice 13medium

Two trains are moving towards each other on parallel tracks. Train A travels at 60 km/h and Train B travels at 40 km/h. If they are currently 150 km apart, in how many hours will they meet?

Practice 14medium

A train passes a stationary pole in 8 seconds. The same train passes a platform of length 240 m in 20 seconds. What is the speed of the train in km/h?

Practice 15medium

Two trains are running towards each other on parallel tracks. Train A travels at 60 km/h and Train B travels at 40 km/h. If they are initially 500 km apart, in how many hours will they meet?

Practice 16medium

A man walks at 5 km/h and a boy cycles at 15 km/h in the same direction on a straight road. If the boy is initially 10 km behind the man, how long will it take for the boy to catch up with the man?

Practice 17medium

Two cyclists start from the same point and travel in opposite directions. Cyclist A travels at 12 km/h and Cyclist B travels at 18 km/h. After how many hours will they be 90 km apart?

Practice 18medium

A car travels from City A to City B at 60 km/h and returns from City B to City A at 40 km/h. If the distance between the cities is 120 km, what is the average speed for the entire journey?

Practice 19medium

Two cyclists start from the same point and travel in opposite directions. The first cyclist travels at 18 km/h and the second at 12 km/h. After how many hours will they be 90 km apart?

Practice 20hard

Two trains start simultaneously from stations A and B, which are 480 km apart. Train X travels from A towards B at 60 km/h, while Train Y travels from B towards A at 40 km/h. A bird flies back and forth between the two trains at a constant speed of 80 km/h, starting from Train X. What is the total distance covered by the bird before the two trains meet?

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60-Second Revision — Relative Speed

  • Formula: Towards each other = S1 + S2, Same direction = |S1 - S2|
  • Remember: Train crossing always needs combined length of both trains
  • Trap: Never forget to convert units - kmph to m/s multiply by 5/18
  • Quick check: Relative speed should make logical sense with given scenario
  • Meeting time = Total distance divided by relative speed
  • Boat speed formulas: Still water = (Down+Up)/2, Current = (Down-Up)/2
  • Always use absolute value when calculating same direction relative speed
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