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That means we have proved the law of impulse(linear momentum)
conservation that states if no external force acts on a closed system of
objects, the momentum of the closed system remains constant

5.2. Center of Mass

The center of mass (the center of inertia) of a system of n- material

points is the point С with radius-vector given by
1 n
r C   m i r (5.6)
i
n  i 1
Where m , is the mass of any material point, r is the radius-vector of
i
i
this material point. The total mass of n material points is given by
n
m   m i r (5.7)
i
 i 1
Let us consider the velocity of the center of mass:

  
 r d C 1 r d i 1  p
v C    m i   m i v i  (5.8)
dt m dt m m

So linear momentum p(impulse) of a closed system is constant,

therefore velocity of centre of
mass under internal forces does
not change. In spite of this

fundamental physical law the
very known Baron
Münchhausen was able to pull

himself and a horse out from
a bog by the hair on his head
(fig.4.2) Оf course, it is a

fantasy as well all other stories
about Baron Münchhausen

Figure 5.2

5.3.Work

The word work is a familiar one, used in many everyday senses. In

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