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.
