The earliest chinese people did not have to worry about invasions from foreign countries because :

Strong army and geography.

Explanation:

The earliest Chinese people did not have to worry about invasions from foreign countries because of their strong army and geography. The Chinese army present in ancient times were very strong and able to defend their lands. Chinese also build china wall in order to protect their lands from the invasion of other people. The geography of china also made difficult for the invaders to capture china.

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