Answer:
Approximately 
. (Assuming that 
, and that the tabletop is level.)
Explanation:
Weight of the book:
.
If the tabletop is level, the normal force on the book will be equal (in magnitude) to weight of the book. Hence, 
.
As a side note, the 
and 
on this book are not equal- these two forces are equal in size but point in the opposite directions.
When the book is moving, the friction 
on it will be equal to
, the coefficient of kinetic friction, times
, the normal force that's acting on it.
That is:
.
Friction acts in the opposite direction of the object's motion. The friction here should act in the opposite direction of that 
applied force. The net force on the book shall be:
.
Apply Newton's Second Law to find the acceleration of this book:
.
Care este problema? Btw why are you speaking Romanian
Answer:
1.6 x 10^-5 T
Explanation:
i = 4 A
r = 0.05 m
The magnetic field due to long wire at a distance r is given by
B = 10^-7 x 2 x 4 / 0.05
B = 1.6 x 10^-5 T
