The distance–time graph shows the
first 70 seconds of a cyclist’s journey. Between which two times is the
cyclist stationary? Explain your answer.
If the cyclist is stationary, then
this means that they are not moving. So no distance will be covered. This section of the distance–time
graph will be flat as the distance will not be changing. Looking at the graph, we can see
that the line is flat in one place, between 30 and 40 seconds.
To explain our answer, we can say
that the gradient of the line is zero at this point. So no distance is travelled. If we recall as well that speed is
equal to distance divided by time, then if the distance travelled is zero, the speed
will also be zero. And if the speed is zero, then the
cyclist is stationary.
Work out the speed of the bike
between zero and 30 seconds. To calculate the speed of the bike
during the first 30 seconds, we need to know both the distance travelled and the
time taken. Reading from the vertical axis, we
see that the distance travelled is 200 metres. And reading from the horizontal
axis, the time taken is 30 seconds. So our calculation for the speed is
200 metres divided by 30 seconds.
We can simplify this fraction by
cancelling a factor of 10 from both the numerator and the denominator. The speed of the bike between zero
and 30 seconds is 20 over three metres per second.