Question

Bhoojho goes to the football ground to play football. The distance- time graph of his journey from his home to the ground is given as the figure:
(a) What does the graph between point B and C indicate about the motion of Bhoojho?
(b) Is the motion between 0 to 4 minutes uniform or non - uniform?
(c) What is his speed between 8 and 12 minutes of his journey?

Answer 1

In this question, we will use the basic relation between time, speed and distance to find the speed. Further, we will use some basic concept of motion to solve the question. We will also learn about the basics of speed and the equations of motion.
Formula used:
$s = \dfrac{d}{t}$

Complete answer:
Here, we can see that graph between the points B and C is parallel to the x-axis as time is changing whereas the distance remains the same, which means there is no motion. Therefore, this shows that Bhoojho is at rest.
In the second case, we can see that the motion between times 0 min to 4 min is non uniform because the graph is not straight. Therefore, It is like two-line joining at point A.
In the last case, we can say that at time 12-minute the distance covered is 225 m and at time 8-minute the distance covered is 150 m, since the speed is given by the distance covered divided by the time taken:
\eqalign{ & speed = \dfrac{{225 - 150}}{{12 - 8}} \cr & \Rightarrow speed = \dfrac{{75m}}{{4\min }} \cr & \therefore speed = 18.75m/\min \cr}
Therefore, the speed in this case is given by the above result.

Additional information:
Speed is the measure of how fast an object can travel, whereas velocity tells us the direction of this speed. Speed is a scalar quantity that means it has only magnitude, whereas velocity is a vector quantity that means it has both magnitude and direction. The S.I unit of velocity is meter per second.
As we know that the equations of motion are equations which describe the behavior of a physical system in terms of its motion as a function of time. Further we can say that these equations of motion describe the behavior of a physical system as a set of mathematical functions in terms of dynamic variables. Here, dynamic variables are said to be normally spatial coordinates and time is used, but others are also possible, like momentum components and time.

Note:
Here, we should remember that the speed and velocity is different i.e., speed is a scalar quantity and velocity is a vector quantity. We should also observe that the equations of motion are only applicable to the classical system not in the quantum system.