This page covers RRB Group D Speed Distance Time with complete concept notes, 3 graded practice MCQs, key points and exam-specific tips. Free to study.
Core ConceptRead this first — the foundation of the topic
Speed, Distance, and Time form the foundation of motion problems in SSC CGL. This topic appears in 2-3 questions per exam and requires strong formula application skills. Core Concept: Speed measures how fast an object moves. Distance is the path covered. Time is the duration taken. These three are linked by a simple relationship that forms the base of all calculations.
Formula BlockMemorise — at least one formula appears in every paper
• Speed = Distance/Time (S = D/T)
• Distance = Speed × Time (D = S × T)
• Time = Distance/Speed (T = D/S)
Unit Conversions (Critical for SSC):
• km/hr to m/s: Multiply by 5/18
• m/s to km/hr: Multiply by 18/5
• 1 km/hr = 5/18 m/s
Exam PatternsWhat examiners ask — read before attempting PYQs
Shortcut 1 - Unit Conversion Trick
To convert km/hr to m/s, multiply by 5/18
Remember
36 km/hr = 10 m/s (this is a standard conversion to memorize)
Shortcut 2 - Distance Formula Rearrangement
When speed increases by x%, new time = Original time × 100/(100+x)
When speed decreases by x%, new time = Original time × 100/(100-x)
Worked ExampleSolve this step-by-step before moving on
Convert to m/s
Speed in m/s = 60 × 5/18 = 300/18 = 16.67 m/s
Answer: 16.67 m/s
Worked Example 2:
A train running at 54 km/hr takes 20 seconds to cross a platform 200m long. Find the length of the train.
1
Step 1
Convert speed to m/s
54 km/hr = 54 × 5/18 = 15 m/s
2
Step 2
Find total distance covered
Distance = Speed × Time = 15 × 20 = 300m
3
Step 3
Find train length
Train length = Total distance - Platform length = 300 - 200 = 100m
Answer: 100 meters
Shortcut 3 - Relative Speed:
• Same direction: Relative speed = |S1 - S2|
• Opposite direction: Relative speed = S1 + S2
Most Common Trap (#1 Mistake):
Students forget unit conversions! SSC deliberately mixes km/hr and m/s in the same question. Always check units in options and convert accordingly. Questions asking for train crossing times usually need m/s, while car journey problems often use km/hr.
Another frequent error is confusing relative motion directions. When two objects move toward each other, add their speeds. When moving in the same direction, subtract speeds.
Time-based problems often trick students with percentage changes in speed. Remember: if speed increases by 25%, time decreases by 20% (not 25%). Use the reciprocal relationship carefully.
Practice identifying whether the question asks for train length, crossing time, or platform length. Each requires different approaches but uses the same core formula.
Key Points to Remember
Master formula: Speed = Distance/Time and its variations D = S × T and T = D/S
Unit conversion: km/hr to m/s multiply by 5/18, m/s to km/hr multiply by 18/5
Standard conversion: 36 km/hr = 10 m/s (memorize this)
Relative speed: same direction subtract speeds, opposite direction add speeds
Train problems: Total distance = Train length + Platform/Bridge length
Speed increase by x%: New time = Original time × 100/(100+x)
Speed decrease by x%: New time = Original time × 100/(100-x)
Always check units in answer options before solving
Average speed = Total distance/Total time (not average of individual speeds)
Time and speed are inversely proportional when distance is constant
Exam-Specific Tips
1 km/hr equals exactly 5/18 m/s
36 km/hr equals exactly 10 m/s
72 km/hr equals exactly 20 m/s
Average speed formula: Total distance divided by total time
Relative speed when objects move toward each other: Sum of individual speeds
Relative speed when objects move in same direction: Difference of individual speeds
When speed increases by 20%, time decreases by 16.67%
When speed decreases by 20%, time increases by 25%
Practice MCQs
Speed Distance Time — Practice Questions
3graded MCQs · easy to hard · full solution & trap analysis
A train travels 240 km in 4 hours at a constant speed. What is the speed of the train in metres per second?
Practice 2medium
A train travels 240 km in 4 hours at constant speed. If the train increases its speed by 20%, how much time will it take to cover the same 240 km distance?
Practice 3hard
A train travels from Station A to Station B, covering the first 120 km at 60 km/h and the next 180 km at 90 km/h. After reaching Station B, it immediately returns to Station A via the same route, but due to maintenance work, its speed on the return journey is reduced by 25%. What is the average speed (in km/h) for the entire round trip?
60-Second Revision — Speed Distance Time
Formula: Speed = Distance/Time, Distance = Speed × Time, Time = Distance/Speed
Remember: 36 km/hr = 10 m/s for quick conversions
Unit conversion: km/hr to m/s multiply by 5/18
Trap: Always check if answer needs km/hr or m/s units
Relative speed: Add for opposite directions, subtract for same direction