AQA GCSE Combined Science (8464), Higher tier · Physics › Forces › Forces and motion › Describing motion along a line
Practise Speed. 13 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
Speed is how fast something is moving, without direction. You need to use s = v t, calculate average speeds for journeys where the speed changes, and recall typical speeds for walking, running, cycling, transport and sound. Expect short calculations and estimates.
Grade by grade
What you need to be able to do, from the first marks up to the top grade.
3
State that speed is a scalarSpeed is the distance travelled per unit time and has no direction.
4
Calculate distance using s = v tFor example, 1.5 m/s for 60 s gives 90 m.
4
Recall typical speeds of everyday motionWalking ~1.5 m/s, running ~3 m/s, cycling ~6 m/s, sound in air ~330 m/s.
5
Rearrange s = v t for speed or timev = s ÷ t and t = s ÷ v.
5
Calculate average speed for a whole journeyAverage speed = total distance ÷ total time.
6
Convert units of distance, time and speedkm to m × 1000, minutes to seconds × 60, km/h to m/s ÷ 3.6.
7
Estimate speeds, distances and timesFor example, walking 1 km at ~1.5 m/s takes about 670 s, roughly 11 minutes.
Notes
What speed is
Speed is the distance travelled per unit time. It does not involve direction, so it is a scalar quantity.
The speed of a moving object is rarely constant. When people walk, run or travel in a car, their speed is constantly changing.
The speed at which a person can walk, run or cycle depends on many factors, including their age, their fitness, the terrain and the distance travelled.
Calculating speed
distance travelled = speed × time: s = v t (for an object moving at constant speed).
s in metres (m), v in metres per second (m/s), t in seconds (s).
When the speed changes during a journey, use average speed = total distance ÷ total time.
To measure a speed, measure a distance (e.g. with a tape measure) and the time taken (e.g. with a stopwatch or light gates), then divide.
Typical speeds to recall
Walking ~1.5 m/s; running ~3 m/s; cycling ~6 m/s.
Car in a town ~13 m/s (30 mph); car on a motorway ~30 m/s (70 mph); fast train ~50 m/s; passenger jet ~250 m/s.
Sound in air ~330 m/s. The speed of sound and the speed of the wind both vary.
The symbol ~ means 'approximately'.
Unit conversions grade 6+
km to m: × 1000. Minutes to seconds: × 60. Hours to seconds: × 3600.
km/h to m/s: × 1000 ÷ 3600, which is the same as ÷ 3.6. So 72 km/h = 20 m/s.
Cheatsheet
s = v t (distance travelled = speed × time)
Units: s in m, v in m/s, t in s
Average speed = total distance ÷ total time
Walking ~1.5 m/s, running ~3 m/s, cycling ~6 m/s
Speed of sound in air ~330 m/s
Car ~13 m/s in a town, ~30 m/s on a motorway
km/h ÷ 3.6 = m/s
Speed is a scalar
How to answer each type of question
Calculate with s = v t
2 to 3 marks4
Convert the time to seconds (and the distance to metres).
Write s = v t, or its rearranged form, and substitute.
Give the answer with a unit.
Example. A cyclist rides at a constant speed of 6.0 m/s for 8.0 minutes. Calculate the distance travelled.
Show the model answer
t = 8.0 × 60 = 480 s (1) s = 6.0 × 480 (1) s = 2880 m (1)
Calculate an average speed
3 marks5
Add up the total distance.
Add up the total time, including any stops that are part of the journey.
Divide, and convert to the units asked for.
Example. A bus travels 3.6 km in 6.0 minutes, stops for 2.0 minutes, then travels 2.4 km in 4.0 minutes. Calculate the average speed of the bus for the whole journey, in m/s.
Show the model answer
total distance = 3.6 + 2.4 = 6.0 km = 6000 m (1) total time = 6.0 + 2.0 + 4.0 = 12.0 min = 720 s (1) average speed = 6000 ÷ 720 = 8.3 m/s (1)
Calculate with the speed of sound (echoes)
2 marks6
For an echo, the sound travels to the surface and back, so double the distance.
Use t = s ÷ v.
Example. A person stands 165 m from a large wall and claps once. speed of sound in air = 330 m/s Calculate the time between the clap and hearing the echo.
Show the model answer
distance travelled by the sound = 2 × 165 = 330 m (1) t = 330 ÷ 330 = 1.0 s (1)
Estimate using typical speeds
2 to 3 marks7
State the typical speed you are using.
Convert units and use s = v t.
Round the answer sensibly and give it in the units asked for.
Example. Estimate how long it takes a student to walk 2 km to school. Give your answer in minutes.
Show the model answer
typical walking speed ~1.5 m/s (1) t = 2000 ÷ 1.5 ≈ 1300 s (1) ≈ 22 minutes (1)
Shortcuts and memory tricks
Formula triangle: s on top, v and t underneath.
m/s to km/h: × 3.6. km/h to m/s: ÷ 3.6.
Sense check with typical speeds: a car at 300 m/s means something has gone wrong.
Echo questions: the sound goes there and back, so double the distance.
Where marks are lost
Not converting minutes or hours into seconds.
Averaging the speeds of the parts of a journey instead of dividing the total distance by the total time.
Leaving out the time spent stopped when the question asks for the average speed of the whole journey.
Forgetting to double the distance in echo questions.
Exam technique
s = v t must be recalled. Here s stands for distance, not speed.
In estimates, state the typical value you used; any sensible value earns the mark.
Check the units the question asks for (m/s, km/h, minutes) before giving your final answer.
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
A student measures the average speed of a toy car as it travels across the floor. Name two measuring instruments the student needs.
A tape measure (or metre rule) and a stopwatch.
Priya travels to college. Priya walks 600 m to a bus stop at a speed of 1.5 m/s and then waits 3.0 minutes for the bus. The bus then travels 4.2 km to the college in 9.0 minutes. Calculate the time Priya takes to walk to the bus stop.
400 s
Write down the equation that links distance travelled (s), average speed (v) and time taken (t), rearranged to give the time.
\(t = \dfrac{s}{v}\)
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 typical speed for a person walking? Tick (✓) one box.[1]
0.15 m/s
1.5 m/s
15 m/s
150 m/s
(b) Which of these is a typical value for the speed of sound in air? Tick (✓) one box.[1]
33 m/s
330 m/s
3300 m/s
300 000 000 m/s
(c) A cyclist rides at a constant speed of 6.0 m/s for 45 s. Calculate the distance travelled by the cyclist. Use the equation: distance travelled = speed × time[2]
Show the answer and mark scheme
(a)Answer: 1.5 m/s
(b)Answer: 330 m/s
(c)Answer: 270 m
s = 6.0 × 45
270 (m)
Question 2Medium7 marks
Priya travels to college. Priya walks 600 m to a bus stop at a speed of 1.5 m/s and then waits 3.0 minutes for the bus. The bus then travels 4.2 km to the college in 9.0 minutes.
(a) Calculate the time Priya takes to walk to the bus stop.[2]
(b) Calculate Priya’s average speed for the whole journey, including the time spent waiting.[3]
(c) The average speed of the bus was 7.8 m/s. Explain why the speed of the bus must have been greater than 7.8 m/s for some of the journey.[1]
(d) Give a typical speed for a person running.[1]
Show the answer and mark scheme
(a)Answer: 400 s
t = 600 ÷ 1.5
400 (s)
(b)Answer: 4.3 m/s
total distance = 600 + 4200 = 4800 (m)
total time = 400 + 180 + 540 = 1120 (s)
average speed = 4800 ÷ 1120 = 4.3 (m/s)
(c)Answer: The bus slowed down or stopped at times, so to average 7.8 m/s it must have gone faster at other times.
the bus stopped or slowed down at times (e.g. at junctions, traffic lights or bus stops), so it must have travelled faster than the average at other times
(d)Answer: About 3 m/s.
3 m/s (allow 2–5 m/s)
Question 3Hard9 marks
During a thunderstorm, a student sees a flash of lightning and hears the thunder 4.5 s later. The speed of sound in air on that day is 340 m/s.
(a) Calculate the distance from the student to the lightning.[2]
(b) Explain why the time taken for the light to reach the student can be ignored.[1]
(c) The student’s timing could be up to 0.5 s too long or too short because of their reaction time. Calculate the range of possible distances to the lightning.[2]
(d) The student sees a second flash of lightning 2.0 minutes after the first flash. The thunder from the second flash is heard 3.0 s after it is seen. Assume that the storm moves in a straight line directly towards the student and that the speed of sound is still 340 m/s. Calculate the speed at which the storm is moving towards the student. Give your answer in km/h.[4]
Show the answer and mark scheme
(a)Answer: 1530 m
s = 340 × 4.5
1530 (m)
(b)Answer: Light travels so much faster than sound that it arrives almost instantly.
the speed of light is very much greater than the speed of sound, so the light arrives almost instantly
(c)Answer: Between 1360 m and 1700 m.
340 × 4.0 = 1360 (m) and 340 × 5.0 = 1700 (m)
between 1360 m and 1700 m
(d)Answer: 15 km/h (15.3 km/h) km/h
distance to the second flash = 340 × 3.0 = 1020 (m)
distance moved by the storm = 1530 − 1020 = 510 (m)