Below is the displacement-time graph of the body with the different points marked:
(a) As we know,
(i) At t = 0 to 5 s
Velocity = Slope of straight line OA
Velocity = AE \over OE
= 3 - 0 \over 5 - 0
= 3 \over 5
= 0.6 m s-1
Hence, velocity at t = 0 to 5 s = 0.6 m s-1
(ii) At t = 5 to 7 s
In this part, we observe that there is no change in the Y axis, (i.e. displacement is zero so the body is stationary).
Hence, velocity at t = 5 to 7 s = 0 m s-1
(iii) At t = 7 s to 9 s
Velocity = Slope of straight line BC
Velocity = CD \over BD
= 7 - 3 \over 9 - 7
= 4 \over 2 = 2 m s-1
(b) As we know,
Average velocity = 7 - 3 \over 9 - 5
= 4 \over 4 = 1 ms-1
Hence, average velocity of the car is 1 ms-1.