AQA GCSE Combined Science Foundation (8464), Foundation tier · Physics › Forces › Forces and motion › Describing motion along a line
Practise Velocity. 6 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
Velocity is speed in a given direction, so it is a vector. You need to explain the difference between speed and velocity.
Key facts
Velocity = speed in a given direction
Velocity is a vector; speed is a scalar
Unit of velocity: m/s, with a direction
Velocity changes if the speed OR the direction changes
Along a line: + for one direction, − for the opposite direction
Notes
Speed and velocity
The velocity of an object is its speed in a given direction.
Velocity is a vector quantity; speed is a scalar quantity.
Velocity has the same unit as speed, m/s, but you also give a direction, e.g. 25 m/s north.
Along a straight line, you can show direction with a sign: +3 m/s forwards, −3 m/s backwards.
When does velocity change?
Velocity changes if the speed changes, if the direction changes, or if both change.
A car going round a bend at a steady 15 m/s has a constant speed but a changing velocity.
Two objects with the same speed moving in different directions have different velocities.
A change in velocity is an acceleration, and it needs a resultant force.
How to answer each type of question
Explain the difference between speed and velocity
2 marksGrade 4
Say that speed is a scalar: magnitude only.
Say that velocity is a vector: speed in a given direction.
Example. Explain the difference between speed and velocity.
Show the model answerHide the model answer
Speed is a scalar: it has magnitude only (1). Velocity is a vector: it is speed in a given direction (1).
Don’t lose marks
Saying velocity is 'the same as speed'.
Giving a velocity without a direction or a sign.
After a bounce, subtracting the speeds (5 − 4 = 1 m/s) instead of the velocities (−4 − 5 = −9 m/s).
More tips
Memory tricks
Velocity = speed + direction.
Steering wheel test: turning the wheel changes your velocity, even if the speedometer reading stays the same.
Exam technique
Whenever a question says 'velocity', think about direction as well as speed.
Use the word 'vector' when you explain what velocity is.
What each grade needs
What you need to be able to do, from the first marks up to the top grade.
Grade 3
Define velocityThe velocity of an object is its speed in a given direction.
Grade 4
Explain the difference between speed and velocitySpeed is a scalar (magnitude only); velocity is a vector (magnitude and direction).
Grade 5
Use + and − signs for velocityAlong a line, e.g. +4 m/s to the right and −4 m/s to the left.
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
What is meant by the velocity of an object?
Its speed in a given direction.
A parcel on a conveyor belt moves 6.0 m to the right in 4.0 s. Calculate its average velocity.
1.5 m/s to the right m/s
A lift moves upwards at a constant 2.5 m/s. Later, the same lift moves downwards at a constant 2.5 m/s. Compare the lift’s speed in the two cases.
The speed is the same in both cases (2.5 m/s).
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy4 marks
(a) Which of these is a velocity? Tick (✓) one box.[1]
20 m/s
20 m/s due north
20 m
20 m due north
(b) What is meant by the velocity of an object?[1]
(c) Two trains pass each other on parallel tracks. Each train travels at 30 m/s, but in opposite directions. Explain why the trains have the same speed but different velocities.[2]
Show the answer and mark scheme
(a)Answer: 20 m/s due north
(b)Answer: Its speed in a given direction.
its speed in a given direction
(c)Answer: Speed has no direction so both are 30 m/s; velocity includes direction and the directions are opposite.
speed has no direction, so both trains have a speed of 30 m/s
velocity includes direction, and the trains move in opposite directions
Question 2Medium6 marks
A swimmer swims one length of a 50 m pool in 40 s. The swimmer then turns and swims back to the start in 45 s.
(a) Calculate the average velocity of the swimmer during the first length. Give the direction.[2]
(b) Calculate the average speed of the swimmer for the two lengths.[2]
(c) What is the average velocity of the swimmer for the two lengths? Explain your answer.[2]
Show the answer and mark scheme
(a)Answer: 1.25 m/s away from the start m/s
50 ÷ 40 = 1.25 (m/s)
away from the start / towards the far end of the pool
(b)Answer: 1.2 m/s (1.18 m/s) m/s
100 ÷ 85
1.2 (m/s) / 1.18 (m/s)
(c)Answer: 0 m/s
zero
the swimmer finishes where they started, so the displacement is zero