Explain why the centrifugal force is a pseudo force?

A long horizontal rod has a bead which can slide along its length, and initially placed at a distance $L$ from one end $A$ of the rod. The rod is set in angular motion about $A$ with constant angular acceleration $\alpha$ . If the coefficient of friction between the rod and the bead is $\mu$ and gravity is neglected, then the time after which the bead starts slipping is

A stone of mass 0.3 kg attached to a 1.5 m long string is whirled around in a horizontal circle at a speed of 6 m/s. The tension in the string is 

A small bead of mass $m=1 \mathrm{kg}$ is carried by a circular hoop having centre at $c$ and radius $r=1 \mathrm{m}$ which rotates about a fixed vertical axis. The coefficient of friction between bead and hoop is $0.5$. The maximum angular speed of the hoop for which the bead does not have relative motion with respect to hoop:

                    

$AB$ is a light rigid rod, which is rotating about a vertical axis passing $A$. A spring of force constant $K$ and natural length $l$ is attached at $A$ and its other end is attached to a small bead of mass $m$. The bead can slide without friction on the rod. At the initial moment the bead is at rest (w.r.t the rod) and the spring is unstrecthed. Select incorrect options :