Study the speed-time graph of a body given below and answer the following questions:
$(i)$ What type of motion is represented by $OA$,$AB$ and $BC$?
(ii) Find positive and negative accelerations of the body.
(iii) Find the distance travelled by the body from $A$ to $B$.

(N/A) $(i)$ $OA$ represents uniform acceleration. $AB$ represents uniform motion (zero acceleration,moving with constant velocity). $BC$ represents negative acceleration (retardation).
(ii) Acceleration is the slope of the graph:
Positive acceleration $(OA)$ = $\frac{6 - 0}{4 - 0} = 1.5 \text{ m s}^{-2}$.
Negative acceleration $(BC)$ = $\frac{0 - 6}{16 - 10} = \frac{-6}{6} = -1 \text{ m s}^{-2}$.
(iii) Distance travelled is the area under the graph between $A$ and $B$:
Distance = $\text{Speed} \times \text{Time} = 6 \text{ m/s} \times (10 - 4) \text{ s} = 6 \times 6 = 36 \text{ m}$.