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:
The angle between the electric field lines and the equipotential surface is 90 degree.
Explanation:
The equipotential surfaces are the surface on which the electric potential is same. The work done in moving a charge from one point to another on an equipotential surface is always zero.
The electric field lines are always perpendicular to the equipotential surface.
As

For equipotential surface, dV = 0 so

The dot product of two non zero vectors is zero, if they are perpendicular to each other.
Answer:
Part a)
%
Part b)
%
Explanation:
As we know that total power used in the room is given as

here we have






Part a)
Since power supply is at 110 Volt so the current obtained from this supply is given as


now resistance of transmission line



now power loss in line is given as



Now percentage loss is given as


%
Part b)
now same power must have been supplied from the supply station at 110 kV, so we have


now power loss in line is given as



Now percentage loss is given as


%
As per energy conservation in the reversible engine we can say

here we know that


now from above equation


now we can convert it into kW


so above is the power input to the refrigerator
now to find COP we know that


so COP of refrigerator is 2.2