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Question Video: Recognizing Non-Uniform Motion Science

The toy car shown was traveling at a uniform speed before we started to measure its speed by recording its position each second. Between which of the following times was the car definitely not uniformly moving at a speed of 1 meter per second? [A] Between the start of measurement and 1 second after the start of measurement [B] Between 1 second after measurement starts and 3 seconds after measurement starts [C] For the whole time that the car moved.

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Video Transcript

The toy car shown was traveling at a uniform speed before we started to measure its speed by recording its position each second. Between which of the following times was the car definitely not uniformly moving at a speed of one meter per second? Is it option (A) between the start of measurement and one second after the start of measurement? Option (B) between one second after measurement starts and three seconds after measurement starts. Or option (C) for the whole time that the car moved.

We recall that the term “uniform speed” means that an object travels the same distance in each time interval for which it moves. This is also known as constant speed and uniform motion. This means that in order to answer this question, we have to determine in which one-second time intervals the car travels a distance of more than one meter or less than one meter in a time interval.

Looking at the diagram, we can see that in the first second after measuring starts, the car travels one meter. This means that it is possible that the car traveled at a uniform speed of one meter per second during this time interval. However, it is not possible for the speed of the car to have been constant for the rest of the journey. We can see from the position of the car two seconds after its position starts being measured that the car has moved more than one meter in one second.

We can also see from the position of the car three seconds after measurement started that the car is moved less than one meter in one second. This means that between one and three seconds after the position of the car starts being measured, the speed of the car varies. And we can therefore conclude that the correct answer is option (B). Between one second after measurement starts and three seconds after measurement starts, the car is definitely not moving uniformly at a speed of one meter per second.

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