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Answer:
A) 0.660 g/ml
B) 1.297 ml
C) 0.272 g
Explanation:
Every substance, body or material has mass and volume, however the mass of different substances occupy different volumes. This is where density 
appears as a physical characteristic property of matter that establishes a relationship between the mass 
of a body or substance and the volume 
it occupies:
(1)
Knowing this, let's begin with the answers:
<h2 /><h2>Answer A:</h2>
Here the mass is 
and th volume 
Solving (1) with these values:
(2)
(3)
<h2>Answer B:</h2>
In this case the mass of a sample is 
and its density is 
.
Isolating from (1):
(4)
(5)
(5)
<h2>Answer C:</h2>
In this case the volume of a sample is 
and its density is 
.
Isolating from (1):
(6)
(7)
(8)
This is easily explained saying that the frictional force between the books and the paper isn't big enough to produce a displacement in the books. The displacement in the books doesn't happen because the frictional force between the books and the surface they are standing on is bigger than the paper's one.
Answer:
We show added energy to a system as +Q or -W
Explanation:
The first law of thermodynamics states that, in an isolated system, energy can neither be created nor be destroyed;
Energy is added to the internal energy of a system as either work energy or heat energy as follows;
ΔU = Q - W
Therefore, when energy is added as heat energy to a system, we show the energy as positive Q (+Q), when energy is added to the system in the form of work, we show the energy as minus W (-W).
