Motion is uniform as graph is straight line. In x-t graph, velocity is tx and the slope of the graph tells the direction of the velocity. Here because of impulse the direction of velocity or slope of the graph changes.During each collisionInitial velocity v1=22=1ms−1Final velocity v2=−22=−1ms−1Impulse = Change in momentum=m∣v2−v1∣=0.4×2=0.8Ns
