$A$ person is using scissors to cut a wire of circular cross-section and negligible weight. The wire slides in the direction away from the hinge until the angle between the scissors blades becomes $2 \alpha$. The friction coefficient between the blades and the wire is:

$A$ block of mass $70\,kg$ is kept on a rough horizontal surface $(\mu = 0.4)$. $A$ person is trying to pull the block by applying a horizontal force,but the block is not moving. The net contact force exerted by the surface on the block is $F$,then

Static friction between two surfaces:

What is the maximum acceleration of a train such that a $50 \ kg$ box lying on its floor remains stationary (in $m \ s^{-2}$)? (Given: Coefficient of static friction between the box and the train's floor is $0.3$ and $g = 10 \ m \ s^{-2}$)

In the figure shown,a block of weight $10 \, N$ is resting on a horizontal surface. The coefficient of static friction between the block and the surface is ${\mu _s} = 0.4$. $A$ force of $3.5 \, N$ will keep the block in uniform motion,once it has been set in motion. If a horizontal force of $3 \, N$ is applied to the block,then the block will:

Is it possible to jump off a perfectly smooth surface? Why?