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

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AcademicPhysicsNCERTClass 7

Given:

Two photographs, shown in Fig. 13.1 and Fig. 13.2, had been taken at an interval of 10 seconds.

To do:

To calculate the speed of the fastest car if a distance of 100 meters is shown by 1 cm in these photographs.

Solution:

Before calculating the speed of the fastest car, we have to determine the car that is moving fastest among all the cars. Let us observe the given two photographs shown in Fig. 13.1 and Fig. 13.2. and determine the fastest moving car.


Determination of the fastest car:

Looking at the second picture, it seems that the blue car is moving at the fastest speed. But look at the 1st and second picture again. It is observed that in 1st picture, the green car was far behind from the blue car and white car. In 2nd picture, it can be clearly seen that the green car overtakes the white car and very close to the blue car.

From the above observation we can conclude that green car is moving fastest among all cars.

Calculation of speed of the fastest moving car:

Distance traveled by blue car $=5\ cm$

Actual distance traveled by green car $=5\times100=500\ m$  [as $1\ cm=100\ m$ given scale]

Time taken $=10\ s$

Therefore, $speed=\frac{distance}{time}$

$=\frac{500\ m}{10\ s}$

$=50\ m/s$

raja
Updated on 10-Oct-2022 13:25:53

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