Calculate speed and specify velocity direction
Connect distance per time to speed and include direction when describing velocity.
Section P1.2 · Motion
Cross-referenced from the related Cambridge IGCSE Chemistry 0620 or Physics 0625 teaching to the 0652 syllabus. Exact 0652 Core/Supplement objective coverage and this final-series course’s examiner fit still need specialist review. Written practice is self-checked and does not predict a Cambridge grade or demonstrate supervised laboratory competence.
Before you begin
- Convert metres, kilometres, seconds and minutes.
- Rearrange a simple equation.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Four minutes is how many seconds?
What you will learn
- Use speed = distance/time with consistent units.
- Distinguish a speed from a directed velocity.
Calculate a rate
Speed is distance travelled per unit time. For a constant-speed journey of 120 m in 15 s, speed is 120/15 = 8 m/s. The unit describes the rate: eight metres are travelled in each second of this motion. Rearranging v = s/t gives s = vt and t = s/v.
Before substituting, make the distance and time units match the requested rate. A distance of 1.2 km is 1200 m and four minutes are 240 s, so the rate is 5 m/s. A speed written in km/h is divided by 3.6 to express the same rate in m/s.
Velocity includes a direction
Velocity is speed in a given direction. Speed 8 m/s can accompany velocity 8 m/s east or 8 m/s west. Those velocities differ despite identical speed magnitudes. A change of direction changes velocity, even if an object's speed remains constant.
When motion includes turns or stops, a single distance/time result is an average speed. Do not assume it was the speed at every instant. The distance travelled is the whole path; a return to the starting point does not erase that distance or imply that the average speed was zero.
Sources for this lesson
Pause and explain
Which statement specifies a velocity?
Worked example
A cyclist covers 1.2 km east at constant speed in four minutes. Find the speed and velocity.
Show the worked solution
- Convert distance to 1200 m and time to 240 s.
- Speed = 1200/240 = 5 m/s.
- Velocity is 5 m/s east.
Answer Speed 5 m/s; velocity 5 m/s east.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
A cyclist covers 1200 m east in 240 s at constant speed. Find speed and velocity.
Give me a hint
Calculate the magnitude first, then add the direction.
Compare my reasoning
- Use v = s/t.
- 1200/240 = 5 m/s.
- Velocity is 5 m/s east.
5 m/s; 5 m/s east.
Look for these in your work
- Divide distance by time.
- Supply velocity direction.
A vehicle moves 72 km/h west. Find its velocity in m/s and distance travelled in 15 s at that constant rate.
Give me a hint
Convert km/h before using seconds.
Compare my reasoning
- 72/3.6 = 20 m/s.
- Velocity is 20 m/s west.
- Distance = 20 × 15 = 300 m.
20 m/s west; 300 m.
Look for these in your work
- Convert the rate.
- Use distance = speed × time.
Two cars move at 12 m/s, one north and one east. Are their speeds and velocities equal?
Give me a hint
Direction changes a velocity but not its speed magnitude.
Compare my reasoning
- Both magnitudes are 12 m/s.
- Their directions differ.
- Speeds are equal; velocities are different.
Equal speeds, different velocities.
Look for these in your work
- Compare magnitudes.
- Compare directions separately.
Common mistakes
- Include direction when a velocity is requested.
- Minutes are not seconds.
- An average rate does not prove constant motion.
What can you explain now?
A train moves 72 km/h east. Express its velocity in m/s.
Compare with the explanation
20 m/s east.
72/3.6 = 20; retain the direction.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Convert a speed into m/s, then write two different velocities with that same magnitude.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.