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zero. The x-component of acceleration can be found from the data of
the velocity acquired in a given time. Since the forces are constant , the
x-acceleration is constant therefore we have the next equation
m
4
v  v 0 s m
a    2
x
t 2s s 2
The resultant of the forces is
    
F  F  F  m g  N ,
fr
x
 
where F frictional force , N - supporting force
fr
 
So that gm  N in component form

F  F  F .
fr
x
Hence we can apply Newton's second law to the block
F  F fr  ma .
x
x
When the block is in motion on the horizontal surface
F fr    mg .

Then
F    mg  ma x  F  m (a   ) g 
x
x
m m
 10kg 2 (  , 0 05 10 )  25N ..
s 2 s 2
4 GRAVITATION

4.1 Newton's law of Universal Gravitation. Kepler's laws .

Gravitation, or gravity, is a natural phenomenon by which
physical bodies attract with a force proportional to their masses.

Gravitation is most known as the agent that gives weight to objects with
mass and makes them fall to the ground when dropped. Gravitation
causes dispersed matter to coalesce, and coalesced matter to remain

intact, thus accounting for the existence of the Earth, the Sun, and most
of the macroscopic objects in the Universe.
Gravitation is responsible for keeping the Earth and the other
planets in their orbits around the Sun; for keeping the Moon in its orbit

around the Earth; for the formation of tides; for natural convection, by
which fluid flows occur under the influence of a gravity; for heating the
interiors of forming stars and planets to very high temperatures; and for

various other phenomena observed on the Earth.

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