原题.(2011年第28届全国中学生物理竞赛预赛第16题)在海面上有3艘轮船,船A以速度u向正东方向航行。船B以速度2u向正北方向航行,船C以速度22~(1/2)u向东偏北45°方向航行.在某一时刻,船B和C恰好同时经过船A的航线并位于船A的前方,船B到船A的距离为a,船C到船A的距离为2a.若以此时刻作为计算时间的零点,求在t时刻B、C两船间距离的中点M到船A的连线 (2011 28th National Physics Contest Contest 16) There are 3 ships on the sea, and ship A sails in the east direction at velocity u. Boat B sails to the north at a speed of 2u and boat C sails eastward at a speed of 45 to the east at a speed of 22-1 / 2u. At any one time, the boats B and C pass exactly simultaneously on the route of the boat A In front of the ship A, the distance between the ship B and the ship A is a, and the distance between the ship C and the ship A is 2a. If the moment is taken as the zero point of the calculation time, find the midpoint M To the ship A connection