What landform blocked contacts between the people in northern china and those in southern china?

Huai River Qin Mountains Line landform blocked contacts between the people in northern China and those in southern China.

Huai River Mountains Line is the landform that is setting out as the dividing line to be located as between the northern and southern China.  It is located at the region of somehow midway between the Yellow River and Yangtze.

a. formula: f=ma or f/m=a

10,000n/1,267kg≈7.9m/

b. formula: a= and s=d/t

speed= 394.6/15

s=26.3m/s

a=

a=1.75m/

c. 7.9-1.75=difference of 6.15m/

d. the force that most likely caused this difference is friction forces