N1 Engineering Science|The Easy Way! 11 Example 1.8 It takes a car 1,5 hours to cover a distance of 170 km. Determine the average speed.


Solution: Given: t = 1,5 × 60 × 60 = 5 400 s


d = 170 × 1 000 = 170 000m v = ?


v = s t = 170 000 5 400 = 31,4 m/s


or speed = 3146060 = 113,3 km/h


, ×× 000


1 Example 1.9


It takes 2 seconds for the sound of thunder to reach a person aſter a flash of lightning. If the velocity of sound is 355 m/s, how far was the bolt of lightning?


Solution: Given: t = 2 s


v = 355 m/s s = ?


1.8.1 Constant velocity/speed


When a body moves at a constant velocity it is oſten useful to represent the relationship between the displacement and time graphically. Te graph will be a straight line and the gradient (or slope) will represent the velocity of the body, fig. 1.5.


Time is usually plotted along the x-axis and any other aspect of motion such as distance or displacement, on the y-axis.


y v = s \s = v × t t


= 355 × 2 = 710m


3s


144444424444443 3t


Time (t) in s Fig. 1.5 Displacement/time graph Te slope (gradient) of a straight line graph is 3 3 3


y x .


In this case, the slope represents the speed of the body: v = 3


s t m/s .................................................................................................................... (1.5)


Fig. 1.5 Displacement/time graph x


Displacement in m


144424443


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