Question

Suppose the two photographs, shown in Figure 13.1 and Figure 13.2, had been taken at an interval of 10 seconds. If a distance of 100 metres is shown by 1 cm in these photographs, calculate the speed of the fastest car.

Figure 13.1 Vehicles moving in the same direction on a road

Figure 13.2 Position of vehicles shown in Figure 13.1 after some time

Answer 1

Figure 13.1 Vehicles moving in the same direction on a road

Figure 13.2 Position of vehicles shown in Figure 13.1 after some time

As we can see from the given figure that green car is the fastest car as it overtakes the white car and is very close to the blue car (initially green car was far behind the blue car).

To calculate the speed of the fastest car i.e. green car, we have scaled road. each marking is of 1 cm.
Distance travelled by a green car, which is measured by scale is 5 cm.
Therefore, 5 cm is equivalent to 500 m.

Distance travelled by car = 500 m

Time interval between the two photographs = 10 s

$$\begin{gathered} \mathrm{Speed}=\frac{\mathrm{Distance}\mathrm{covered}}{\mathrm{Time}\mathrm{taken}} \\ =\frac{500}{10} \\ =50\mathrm{m}/\mathrm{s} \end{gathered}$$

So, the speed of fastest car is 50 m/s