Answer:
The valves prevent the backward flow of blood. These valves are actual flaps that are located on each end of the two ventricles (lower chambers of the heart). They act as one-way inlets of blood on one side of a ventricle and one-way outlets of blood on the other side of a ventricle.
Explanation:
Answer: the answer would be four thousand
Explanation: hope this helps
Answer:
The magintude of the acceleration for both objects is 
Explanation:
Drawing a free body diagram on the two boxes we can analyze the system more easily.
we can take the acceleration going up as positive for reference purposes.
for mA let's suppose that is ascending so:

and for mB (descending):


because the two boxes has the same acceleration because they are attached together:

So the magintude of the acceleration for both objects is 