The limiting friction between two bodies in contact is independent of

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:

$A$ box of mass $2 kg$ is placed on the roof of a car. The box would remain stationary until the car attains a maximum acceleration. The coefficient of static friction between the box and the roof of the car is $0.2$ and $g=10 ms^{-2}$. This maximum acceleration of the car, for the box to remain stationary, is: (in $ms^{-2}$)

The blocks $A$ and $B$ are arranged as shown in the figure. The pulley is frictionless. The mass of $A$ is $10 \, kg$. The coefficient of friction of $A$ with the horizontal surface is $0.20$. The minimum mass of $B$ to start the motion will be...... $kg$.

As shown in the figure, a block of mass $10 \ kg$ lying on a horizontal surface is pulled by a force $F$ acting at an angle $30^{\circ}$ with the horizontal. For $\mu_{s} = 0.25$, the block will just start to move for the value of $F$: [Given $g = 10 \ ms^{-2}$] (in $N$)

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