1. From the position time graph we can see that the particle is in rest during t < 0 and t > 4. Hence net force on it is zero t < 0, t > 4 s. During 0 < t < 4; the graph has a constant slope i.e, particle has uniform velocity = 3/4 = 0.75 m/s.
Hence net force is zero.
2. at t = 0 u = 0 v = 0.75
impulse = change in momentum
= M (v – u) = 4 (0.75 – 0)
= 3 kg m/s
at t = 4, u = 0.75 v = 0
impulse = 4 (0 – 0.75) = – 3 kg m/s.