The speed-time graph for a car is shown is Figure

(a) Find how far does the car travel in the first `4` seconds. Shade the area on the graph that represents the distance travelled by the car during this period.
(b) Which part of the graph represents uniform motion of the car ?

Explanation

(a) From the speed time graph shown in Figure, we find that speed of the body goes on increasing from `t = 0` to `t = 6 s`. As the speed time graph is not a straight line, therefore, acceleration of the body is not uniform.
The distance travelled by the car in the first four second is given by the area enclosed by the speed time graph and X-axis from `t = 0` to `t = 4s`. This has been lightly shaded in the graph.
To calculate the distance, in such cases, we actually count the number of squares in the shaded portion of the graph. It comes out to be `320.5` squares. As one square on X-axis represents `t = (1)/(6)s` and one square on Y-axis represents `v = (1)/(3)m//s`, therefore, area of each square `= v xx t = (1)/(3) xx (1)/(6) = (1)/(18)m`.
Total area of `320.5` squares `= 320.5 xx (1)/(18)m = 17.80 m`
This is the distance travelled by the car in first four seconds.
(b) In uniform motion, speed of the body becomes constant. The portion of the graph from `t = 6s` to `t = 10 s` represents uniform motion of the car.