Here, m=0.04kg. Position time graph shows that the particle movesfrom x=0 at O to x=2cm at A in 2 s.
As x-t graph is a straight line, the motion is with a constant velocity
u=

(2−0)cm

(2−0)s

=1cms−1=10−2ms−1
From x=2cm at A, particle goes to x=0 at B in 2 s.
As AB is a straight line, motion is with constant velocity
v=

(0−2)cm

(4−2)s

=−1cms−1=−10−2cms−1
Negative sign indicates the reversal of direction of motion. This is being repeated. We can visualise a ball moving between two walls located at x = 0 and x = 2 cm, getting rebounded repeatedly on striking against each wall. On every collision with a wall, linear momentum of the ball changes.
Therefore, the ball receives impulse after every two seconds.
Magnitude of impulse = total change in linear momentum
=mu−mv=m(u−v)
=0.04[10−2−(−10−2)]
=0.04(10−2+10−2)
=0.08×10−2=8×10−4‌kg‌m‌s−1