A distance time graph will tell you at any point how far has been travelled in a certain direction. Distance time graphs assume the direction of travel does not change. If it does this will not be shown on the graph.
On a distance time graph we can use the following gradient=velocity,
A typical question will be: A car travels at
for 1.5 hours then stops at a service station for 20 minutes. It continues it's journey and travels another 70 km to it's destination, arriving in a further 70 minutes.
a}Sketch a distance - time graph to illustrate the car's journey.
b)Find the average speed.
During the first 1.5 or 90 minutes hours the car travels
The graph will start from the origin at go up to the point (90,150). During the next 20 minutes the car will not be moving, so the car will be a constant distance – ie the graph will be a horizontal line for this period We can draw astraigh line to the point (90,150)+(20,0)=(110,150). In the last part of the journey the car travels 70 km in 70 minutes. It's final position will be at the point (110,150)+(70,70)=(180,220).
Typically we have to express the speed in
To do this we reflect that since there are 60 minutes in an hour, the average speed of the car can be written