V PT = velocity of the Passenger relative to the Train = + 2.0 m/s
V TG = velocity of the Train relative to the Ground = + 9.0 m/s
V PG = velocity of the Passenger relative to the Ground = + 11 m/s
V PG = V PT + V TG
Thus V PG = (2.0 m/s) + (9.0 m/s) = + 11 m/s
那么同理
V BW = velocity of the Boat relative to the water
V WS = velocity of the Water relative to the Shore
V BS = velocity of the Boat relative to the Shore
Thus V BS = V BW + V WS