Speed, distance and time

Using the speed, distance and time formulas, average speed for trips with several parts, and distance-time graphs.

The formulas

Speed, distance, time

$$S = \frac{D}{T} \qquad D = S \times T \qquad T = \frac{D}{S}$$

Distance-time graph

The steeper the line, the faster the speed. The gradient of a distance-time graph is the speed.

Example 1●

A car travels $210$ km in $2.5$ h. Find its average speed.

$S = 210 \div 2.5 = 84$ km/h

Example 2●●

How long does it take to cycle $27$ km at $18$ km/h? Give hours and minutes.

$T = 27 \div 18 = 1.5$ h

$= 1$ h $30$ min

Flashcards

Speed formula

$S = D \div T$

Gradient of a distance-time graph

Speed

$0.25$ h

$15$ min

Practice

$210$ km in $2.5$ h. Average speed (km/h)?
$27$ km at $18$ km/h. Time in hours?
Distance travelled in $3$ h at $90$ km/h?
A runner covers $100$ m in $5$ s. Speed in m/s?
A trip is $60$ km in $1$ h then $30$ km in $1$ h. Average speed (km/h)?
How many minutes to travel $50$ km at $75$ km/h?
On a distance-time graph, a horizontal line means:
A car goes $120$ km at $60$ km/h, then $120$ km at $40$ km/h. Average speed for the trip?