Question

Distance - time graph of an object is shown in the figure. Object moves with constant speed in a time interval from

Answer 1

We know that the distance-time graph of the motion of an object moving with a contant speed is always a straight line.
Here, from $t_0$ to $t_1$, the distance covered by the object is zero. Therefore, object is at rest.
From $t_1$ to $t_2$, distance covered is increasing with time, which means object is moving with some speed. Also the graph is a straight line, therefore speed is constant.

From $t_2$ to $t_3$ and $t_3$ to $t_4$, the graph is not a staright line, therefore, speed is not constant.