Question

The position - time graph for a particle moving along a straight line is shown in figure.The total distance travelled by it in time t =0 to t=10s is

Answer 1

The answer is 20.
You can see that in first two seconds it covers 10m then it stops and after that, moves back to mean position.
However, if one asks about displacement, it'd be 0.

Answer 2

During the time interval 0 to 2 seconds, the particle travels from 0 to 10 meters.

During the time interval 2 to 4 seconds, 4 to 6 seconds, 6 to 8 seconds, the particle covers no distance as it is shown by the straight horizontal line.

During the time interval 8 to 10 seconds, the particle travels back to the mean position covering another 10 meter.

Hence the total distance covered during the time intervals (0-2, 2-4, 4-6, 6-8, 8-10) = 10+ 0+ 0+ 0+ 10  = 20 meters.