Question Video: Recognizing When an Object Has the Greatest Average Speed | Nagwa Question Video: Recognizing When an Object Has the Greatest Average Speed | Nagwa

# Question Video: Recognizing When an Object Has the Greatest Average Speed Science • Third Year of Preparatory School

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The speed of a toy car is measured by recording its position each second. Between which of the following times is the average speed of the car the greatest? [A] From when measuring starts to 1 second after measuring starts [B] From 1 second after measuring starts to 2 seconds after measuring starts [C] From 2 seconds after measuring starts to 3 seconds after measuring starts

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### Video Transcript

The speed of a toy car is measured by recording its position each second. Between which of the following times is the average speed of the car the greatest? (A) From when measuring starts to one second after measuring starts. (B) From one second after measuring starts to two seconds after measuring starts. (C) From two seconds after measuring starts to three seconds after measuring starts.

We’ve been given a diagram here showing a toy car that’s moving to the right. Specifically, we’re shown the position of the car at four different times as it moves. The car begins its journey over here at the very instant we start the measurement. Then, one second later, we can see that the car has moved to the right. After one more second has passed, the car has moved further to the right. And then we can also see the car’s position after yet one more second has passed at the final moment of measurement. Here, a total of three seconds have passed.

As the car moves, we can roughly track how far it goes using these one-meter markings up above. Remember that the car moves over three one-second intervals. From the diagram, we can see that the car moves a different distance over each one-second interval. We can recall that if an object does not travel equal distances in equal intervals of times, then it does not move at a constant speed. Rather, we say that the car moves with variable speed. This means that the car moves at different speeds at different times. And this question is simply asking us when did the car move the fastest.

To answer this, we need to compare the speed of the car during each of the one-second intervals. Let’s recall that the average speed of an object over a given amount of time is equal to the distance traveled divided by the time over which that distance is traveled. In this case, all of the time intervals are one second long. So, to compare the car’s speed during those time intervals, we only need to look at the distance the car traveled in each interval. The car must have traveled at the greatest average speed during the one-second interval when it traveled the greatest distance.

So, the question is, during which time interval did the car travel the greatest distance? Looking at the diagram, we see that the car traveled the greatest distance between one second after measuring starts and two seconds after measuring starts. In the first interval, the car travels one meter. In the second interval, the car travels a distance greater than one meter. In the third interval, the car travels less than one meter. So we see that this second interval, between one and two seconds after measuring starts, is the only one in which the distance traveled is greater than one meter. Since the car travels the greatest distance in this interval, then we know that the car had the greatest average speed in this interval between one and two seconds after measuring starts.

Our answer then is option (B). The car has the greatest average speed from one second after measuring starts to two seconds after measuring starts.

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