Answer:

Explanation:
Given that,
The radius of sphere, r = 5 cm = 0.05 m
Net charge carries, q = 7.5 µC = 7.5 × 10⁻⁶ C
We need to find the surface charge density on the sphere. Net charge per unit area is called the surface charge density. So,

So, the surface charge density on the sphere is
.
Answer:
W = -510.98J
Explanation:
Force = 43N, 61° SW
Displacement = 12m, 22° NE
Work done is given as:
W = F*d*cosA
where A = angle between force and displacement.
Angle between force and displacement, A = 61 + 90 + 22 = 172°
W = 43 * 12 * cos172
W = -510.98J
The negative sign shows that the work done is in the opposite direction of the force applied to it.
Answer:
1. The force of the shelf holding the book up.
Explanation:
The free body diagram of the book is as follows:
1 - The weight of the book towards downwards
2 - The normal force that the shelf exerts on the book towards upwards.
Since the book is at rest, these two forces are equal to each other and according to Newton's Third Law the reaction force to the force of gravity is equal but opposite to the weight of the book. This reaction force is the one that holds the book up on the shelf.