Question Video: Comparing Thinking and Braking Distances for a Car | Nagwa Question Video: Comparing Thinking and Braking Distances for a Car | Nagwa

Question Video: Comparing Thinking and Braking Distances for a Car Physics • First Year of Secondary School

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The thinking distance and braking distance of a car at different initial speeds are shown in the graph. The thinking distance is in blue and the braking distance is in orange. How much greater is the braking distance than the thinking distance when the initial speed is 90 km/h?

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Video Transcript

The thinking distance and braking distance of a car at different initial speeds are shown in the graph. The thinking distance is in blue and the braking distance is in orange. How much greater is the braking distance than the thinking distance when the initial speed is 90 kilometers per hour?

In this question, we are shown a graph that plots the thinking distance and braking distance for a car at different initial speeds. We want to find the braking distance and thinking distance for this car when it has an initial speed of 90 kilometers per hour and determine how much greater the braking distance is than the thinking distance.

On this graph, let’s mark the point on the 𝑥-axis that corresponds to an initial speed of 90 kilometers per hour. Now let’s draw a dashed vertical line from 90 kilometers per hour up to the blue and orange lines. Remember that the thinking distance is shown in blue and the braking distance is shown in orange. If we now draw a dashed horizontal line from the orange line to the 𝑦-axis, we will be able to find out the braking distance of the car by reading the value off the 𝑦-axis. After drawing this dashed horizontal line, we see that the braking distance for the car with an initial speed of 90 kilometers per hour is 45 meters.

Now let’s work out the thinking distance. If we draw a dashed horizontal line from the blue line to the 𝑦-axis, we can read off a value of 37 meters for the thinking distance of the car when it has an initial speed of 90 kilometers per hour.

We want to calculate how much greater the braking distance is than the thinking distance when the initial speed is 90 kilometers per hour. So we simply need to do the calculation braking distance minus thinking distance. Substituting the values of braking distance and thinking distance into this equation, we find that the difference between the two is equal to 45 meters minus 37 meters, which is equal to eight meters.

Thus, we have arrived at the correct answer. The braking distance is eight meters greater than the thinking distance when the car’s initial speed is 90 kilometers per hour.

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