A particle moves along a straight line such that its velocity varies with time as follows:
• at t=0s, v=30m/s;
• it decreases uniformly to v=0 at t=3s;
• without any change in magnitude of acceleration, it continues to v=−20m/s at t=5s;
• it then moves with this constant velocity up to t=9s.
Taking the starting point as the origin and positive velocity as the positive direction, the displacement of the particle at t=9s is
(a) −35m
(b) +55m
(c) −55m
(d) −25m