Velocity - time (v-t) graph for a moving object is shown in the figure. Total displacement (in m) of the object during the time interval when there is non-zero acceleration and retardation is $\_\_\_\_\_\_$

Between time interval of 20s to 40 s, there is non-zero acceleration and retardation.

Hence, the distance traveled during this interval
=  Area between time interval 20 s to 40 s
=1/2 × 20 × 3 + 20×1 = 30 + 20 = 50m