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 ........ $^o$

What is the minimum number of forces acting in the same plane on a particle that can result in a zero net force?

Two equal heavy spheres,each of radius $r$,are in equilibrium within a smooth cup of radius $3r$. The ratio of the reaction between the cup and one sphere to that between the two spheres is:

One end of a horizontal uniform beam of weight $W$ and length $L$ is hinged on a vertical wall at point $O$ and its other end is supported by a light inextensible rope. The other end of the rope is fixed at point $Q$,at a height $L$ above the hinge at point $O$. $A$ block of weight $\alpha W$ is attached at the point $P$ of the beam,as shown in the figure. The rope can sustain a maximum tension of $(2 \sqrt{2}) W$. Which of the following statement$(s)$ is(are) correct?

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.

Can a stationary object remain stationary if multiple external forces act upon it?