A distance-time graph shows how the distance travelled by an object changes over time and can be used to calculate the speed of the object. A sloping line on a distance-time graph shows that the ...

To work out the time, divide distance by speed. The distance travelled in 1 hour is the speed in miles per hour. To calculate the speed, divide the distance in miles (180) by the time in hours (3).

Correct. As you would expect, twice the speed equals twice the stopping time. Now here's the catch. Say that same car going thirty required a hundred feet of skidding distance before stopping.