A motorboat went upstream at a constant speed. When it arrived at a certain place, it found that it had lost a lifebuoy, immediately turned around and chased along the river at the same speed.

The distance from finding the lost lifebuoy to finding it is s = s1+S2 = (v+u) t; ②

T 1 The distance traveled by motorboats is s1= (v-u) t1; ③

Three types can be obtained simultaneously: v = 2s1+s22t1;

u = s22t 1；

After arriving at point B, the distance to point C is S2;

So S2 = (v+u) t2;

T2 = S2V+U = s22s 1+s22t 1+s22t 1 = t 1。

Answer: the speed v of motorboat is 2s1+s22t1; The flow velocity u is s22t1; After arriving at point B, find the lifebuoy through t 1