$A$ body under the action of several forces will have zero acceleration:

$A$ book is lying on a table. What is the angle between the normal reaction acting on the book on the table and the weight of the book (in $^\circ$)?

Why are the states of a body at rest and a body moving with constant velocity considered equivalent in terms of net force?

The resultant of two forces,one double the other in magnitude,is perpendicular to the smaller of the two forces. The angle between the two forces is ........ $^o$

Ten one-rupee coins are placed on top of each other on a table. Each coin has a mass $m$. Give the magnitude and direction of:
$(a)$ The force on the $7^{\text{th}}$ coin (counted from the bottom) due to all the coins on its top.
$(b)$ The force on the $7^{\text{th}}$ coin by the $8^{\text{th}}$ coin.
$(c)$ The reaction of the $6^{\text{th}}$ coin on the $7^{\text{th}}$ coin.

When is a body said to be in mechanical equilibrium?