Unit 18 Section 1 : Speed

In this section we introduce the idea of speed, considering both instantaneous speed and average speed.
Instantaneous speed = speed at any instant in time
Average speed =
distance travelled
time taken
If a car travels 100 miles in 2 hours:
Average speed =
100 miles
2 hours
= 50 miles per hour (mph)
The car does not travel at a constant speed of 50 mph; its speed varies during the journey between 0 mph and 70 mph.
The speed at any particular time is called the instantaneous speed.

The following table lists units in common use for speed and their abbreviations:

Example Questions

Example Question 1
Judith drives from Plymouth to Southampton, a distance of 160 miles, in 4 hours.
She then drives from Southampton to London, a distance of 90 miles, in 1 hour and 30 minutes.

Determine her average speed for each journey.

For the Plymouth to Southampton journey, we divide 160 miles by 4 hours.
Her average speed on this part of the journey was 40 mph.

For the Southampton to London journey, we divide 90 miles by 1.5 hours.
Her average speed on this part of the journey was 60 mph.

Example Question 2
John can type 960 words in 20 minutes.

(a) Calculate his average typing speed in words per minute.
To work this out, we divide 960 words by 20 minutes.
His average typing speed is 48 words per minute (wpm).

(b) Calculate his average typing speed in words per hour.
If he can type 48 words per minute, then he can type 60 times as many in an hour.
His average typing speed is 2880 words per hour (because 60 48 = 2880).

Practice Question

Work out the answer to these questions then click on the button marked Click on this button below to see the correct answer to see whether you are correct.

A marathon runner completed 24 miles in 4 hours.

(a) What was their average speed in miles per hour?

(b) What was their average speed in miles per minute?

 

Exercises

Work out the answers to the questions below and fill in the boxes. Click on the Click this button to see if you are correct button to find out whether you have answered correctly. If you are right then will appear and you should move on to the next question. If appears then your answer is wrong. Click on to clear your original answer and have another go. If you can't work out the right answer then click on Click on this button to see the correct answer to see the answer.

Question 1
Peter drives 320 miles in 8 hours.

Calculate his average speed.
mph

Question 2
Daisy drives from Sheffield to London, a distance of 168 miles, in 4 hours.

Calculate her average speed.
mph

Question 3
A snail moves 8 m in 2 hours.

Calculate the average speed of the snail in metres per hour.
m/hr

Question 4
A lorry driver keeps a record of each journey he makes.
Complete the average speed for each journey in the table below.
Start Finish Start Time Finish Time Distance Average Speed
(a) Brighton Norwich 0800 1200 172 miles mph
(b) Norwich Carlisle 1400 1900 280 miles mph
(c) Carlisle Cardiff 1000 1800 300 miles mph
(d) Cardiff Exeter 0700 0930 120 miles mph
(e) Exeter Brighton 1030 1530 175 miles mph
Question 5
Javinda takes 1½ hours to drive 30 km in the rush hour.

Calculate his average speed in km/h.

Question 6
Rebecca cycles 20 miles on her bike in 2 hours and 30 minutes.

Calculate her average speed in mph.

Question 7
Julie can type 50 words in 2 minutes.
Debbie can type 300 words in 15 minutes.

(a) What is Julie's typing speed in words per minute?
wpm

(b) What is Julie's typing speed in words per hour?
wphr

(c) What is Debbie's typing speed in words per minute?
wpm

(d) What is Debbie's typing speed in words per hour?
wphr

Question 8
Fatima, Emma and Andy each drive from London to Brighton, a distance of 60 miles.
Fatima takes 1 hour, Emma takes 2 hours and Andy takes 1½ hours.

Calculate the average speed for:
(a) Fatima mph
(b) Emma mph
(c) Andy mph

Question 9
Eva drives from Edinburgh to Dover in 3 stages. Calculate her average speed for each stage of her journey.
Journey Start Time Finish Time Distance Average Speed
(a) Edinburgh to Leeds 0620 0920 210 miles
(b) Leeds to London 1035 1305 200 miles
(c) London to Dover 1503 1703 78 miles
Question 10
Delia drives 220 km in 3½ hours.

Calculate her average speed correct to the nearest km/h.
km/h


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Produced by A.J. Reynolds August 2008