Question

1
select the correct answer.
the motion of a car on a position-time graph is represented with a horizontal line. what does this indicate about the car’s motion?
a. it’s not moving.
b. it’s moving at a constant speed.
c. it’s moving at a constant velocity.
d. it’s speeding up.

Explanation:

In a position - time graph, the slope of the line represents the velocity (or speed, in the case of magnitude) of the object. The formula for the slope ($m$) of a line in a position - time graph is $m=\frac{\Delta x}{\Delta t}$, where $\Delta x$ is the change in position and $\Delta t$ is the change in time. For a horizontal line, the change in position $\Delta x = 0$ (because the $y$ - value, which represents position, does not change as time $t$ (the $x$ - value) changes). If $\Delta x = 0$, then the slope (velocity) is $0$. A velocity of $0$ means the object is not moving. Option B is incorrect because a constant speed would be represented by a straight line with a non - zero constant slope. Option C is incorrect because constant velocity (which includes speed and direction) would also be a straight line with non - zero slope (if speed is non - zero) or zero slope (but zero slope means no motion, not constant velocity in the sense of moving). Option D is incorrect because speeding up would be represented by a curve with an increasing slope (or a line with increasing slope in the case of constant acceleration), not a horizontal line.

Answer:

A. It's not moving.