The particles in a liquid are extremely fast, not faster than a gas, but faster than a solid. The way the particles move allow you to get volume but not area for it doesn't have a defiant shape
explanation
a=average velocity/average time
average velocity=0.0+1.2+2.4+3.6/4
average velocity=7.2/4
average velocity=1.8 m/s
average time=0.0+3.0+6.0+9.0/4
average time=18/4
average time=4.5 s
a= average velocity/average time
a=1.8/4.5
a=0.4 m/s²
I believe that number 2 is A, not sure though.
B)
The speed of the cart changed because it stopped.
Hope I could help!
-Marshy