Answer:
1.65
Explanation:
The equation of the forces along the horizontal direction is:
(1)
where
F = 65 N is the force applied with the push
is the frictional force
m = 4 kg is the mass
is the acceleration
The force of friction can be written as 
(2), where
is the coefficient of kinetic friction
R is the normal force exerted by the floor
The equation of forces along the vertical direction is
(3)
since the bookcase is in equilibrium. Substituting (2) and (3) into (1), we find
And solving for ,
Answer:
C
Explanation:
A theory can be changed when new evidence is found. A law doesn't change because it is universally a fact. It doesn't need new evidence to support it.
D)
(()(){({)({)(()({)())({)()({)()()()9
The gravitational potential energy of an object depends on three things. Its mass, its height above the surface of the earth and the pull of gravity (which is assumed to always be 9.8 m/s².
The Formula for finding the GPE is : m x g x h where m = mass, g = gravitational acceleration and h is height from earth's surface.
Using this formula we can find that :
GPE= 75 x 9.8 x 300 = 220500J (where J is the SI unit for GPE and stands for Joules.
