Question

Whenever an object moves with a constant speed, its distance-time graph is a
(A) Parabola
(B) Straight line, perpendicular to the time axis
(C) Straight line, parallel to the time axis
(D) Straight line passing through origin

Answer 1

An object is moving with constant velocity. If we plot a distance-time graph of the object, the Y-axis will represent the distance travelled by the object and the X-axis will represent the time. Here we have to find the nature of the plot when the object is moving with constant speed.

Complete step by step solution:
For a moving object the position coordinate changes with time.
The object is claimed to be moving with constant speed.
We plot the distance-time graph with distance on the Y-axis and time on the X-axis.
We know that the formula for speed can be written as,
$s = \dfrac{d}{t}$
Where $s$ stands for the speed of the object, $d$ stands for the distance travelled by the object and $t$ stands for the time taken by the object to travel $d$ distance.
From the above equation we can write
$d = st$
It is given that the speed $s$ is constant.
Therefore if we plot we get a $Y = mX$ , where $m$ is a constant type of plot. This is a line passing through the origin.
Therefore, The answer is: Option (D): Straight line passing through origin.

Additional information:
A position-time graph can be used to find the position of the object at any instant of time, to find the velocity of the object at any instant of time and to obtain the nature of the motion.

Note
For a body moving with constant positive velocity the position coordinate increases continuously. For a body moving with constant negative velocity the position coordinate decreases continuously. If an object covers equal distances in equal intervals of time, no matter how small the interval is, then the object is said to have uniform speed.