If the resultant of $n$ forces of different magnitudes acting at a point is zero,then the minimum value of $n$ is

Which of the following sets of concurrent forces may be in equilibrium?

$A$ block is placed between two surfaces as shown in the figure. Find the normal reaction at both surfaces. [Assume $g = 10 \ m/s^2$]

$A$ small sphere is hung by a string fixed to a wall as shown in the figure. The sphere is pushed from the wall by a stick. The forces acting on the sphere are as shown. Then,identify the incorrect expression.

$A$ block is being pulled by a force $F$ on a long frictionless level floor. The magnitude of the force is gradually increased from zero until the block lifts off the floor. Immediately after the block leaves the floor,its acceleration is

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.