Suppose that the aorta has a radius of about 1.25 cm and that the typical blood velocity is around 30 cm/s
and that it has an average density of 1050 kg/m^3.
(a) What is the average blood velocity in the major
arteries if the total cross-sectional arca of the major
arteries is 20 cm^2,
(b) What is the total flow rate?
(c) If the blood in the circulatory system goes through
the capillaries, what is the total cross-sectional area
of the capillaries if the average velocity of the
blood in the capillaries is 0.03 cm/s?
(d) If a typical capillary has a cross-sectional area of 3
X 10^-11 m^2. about how many capillaries are there
in the human body?
(e) What is the kinetic energy per unit volume for blood
in the aorta, the major arteries, and the capillaries?
(f) If a capillary has an average length of 0.75 mm
what is the average time that a red blood cell
remains in a capillary?

the box does not move because you need to use a force greater than 300 n. you are only using 50 n. it needs to at least be 301 n for the box to move because then it is an unbalanced force and it will move the way that the greater force is pushing it. if you use only 300 n it will be a balanced force and will not move because the force you are exerting on the   box is the same as its force.

hope this !

im sorry if i went too in depth, i am going to include a link to a video on khan academy that will explain this.   hope that you like the video and that it explains more in detail to you.

that is the link.

when two balls of the different masses are dropped from equal height, they reach the ground at the same time .this is because they experience the same acceleration.

the acceleration is independent of mass.

thus when they are dropped they will always maintain the same velocity and travel the same distance (neglect air resistance of course) at the same time.