List of top Physics Questions on Equilibrium of a particle

Figure 4.16 shows the position-time graph of a particle of mass 4 kg. What is the 

1. force on the particle for t < 0, t > 4 s, 0 < t < 4 s? 
2. impulse at t = 0 and t = 4 s ? 
   (Consider one-dimensional motion only).