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
14graded MCQs · easy to hard · full solution & trap analysis
A cyclist covers 180 metres in 9 seconds. What is the cyclist's speed in m/s?
Practice 2easy
A train travels at 72 km/h. How far will it travel in 5 hours?
Practice 3easy
A person walks 150 metres in 30 seconds. How long will it take to walk 450 metres at the same speed?
Practice 4easy
A bus covers 360 km in 6 hours. If it travels at the same speed, how much distance will it cover in 9 hours?
Practice 5easy
A runner completes 800 metres in 160 seconds. What is the runner's speed in m/s?
Practice 6easy
A car travels 240 km in 4 hours. What is its speed in km/h?
Practice 7medium
A boat travels 48 km downstream in 3 hours and 48 km upstream in 6 hours. What is the speed of the boat in still water?
Practice 8medium
A cyclist covers 180 km in 5 hours. A car covers the same distance in 3 hours. What is the ratio of their speeds?
Practice 9medium
A person travels from City P to City Q, a distance of 300 km. He covers the first 150 km at 50 km/h and the remaining 150 km at 75 km/h. What is his average speed for the entire journey?
Practice 10medium
Two trains start from the same station at the same time. Train A travels at 60 km/h and Train B travels at 80 km/h in the same direction. After how many hours will Train B be 100 km ahead of Train A?
Practice 11hard
A boat takes 6 hours to travel 120 km downstream and 8 hours to travel the same distance upstream. If the boat's speed in still water is b km/h and the current's speed is c km/h, what is the value of b?
Practice 12hard
A car travels from City X to City Y at a speed of 60 km/h. On the return journey, due to traffic, it travels at 40 km/h. If the total time taken for the round trip is 10 hours, what is the distance between City X and City Y?
Practice 13hard
Two cyclists start simultaneously from the same point and travel in the same direction. Cyclist A travels at 24 km/h and Cyclist B travels at 32 km/h. After how much time will Cyclist B be exactly 40 km ahead of Cyclist A?
Practice 14hard
A person walks from Point P to Point Q at 4 km/h and returns from Q to P at 6 km/h. The total time taken for the round trip is 5 hours. What is the distance between P and Q?
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