Which one of the following is not used to reduce friction?

In the figure,a ladder of mass $m$ is shown leaning against a wall. It is in static equilibrium making an angle $\theta$ with the horizontal floor. The coefficient of friction between the wall and the ladder is $\mu_1$ and that between the floor and the ladder is $\mu_2$. The normal reaction of the wall on the ladder is $N_1$ and that of the floor is $N_2$. If the ladder is about to slip,then

$A$ parachutist of weight $w$ strikes the ground with his legs fixed and comes to rest with an upward acceleration of magnitude $3g$. The force exerted on him by the ground during landing is:

$A$ ball is dropped on the floor from a height of $20 \ m$. It rebounds to a height of $5 \ m$. The ball remains in contact with the floor for $1 \ s$. The average acceleration during contact is (acceleration due to gravity $g = 10 \ m/s^2$): (in $m/s^2$)

$A$ truck starting from rest moves with an acceleration of $5\,m/s^2$ for $1\,sec$ and then moves with constant velocity. The velocity w.r.t. ground v/s time graph for the block in the truck is (Assume that the block does not fall off the truck and the coefficient of friction $\mu = 0.2$):

$A$ $\sqrt{34}\,m$ long ladder weighing $10\,kg$ leans on a frictionless wall. Its feet rest on the floor $3\,m$ away from the wall as shown in the figure. If $F_{f}$ and $F_{w}$ are the reaction forces of the floor and the wall,then the ratio of $F_{w}/F_{f}$ will be:
(Use $g=10\,m/s^{2}$)