Statement-1: It is easier to pull a heavy object than to push it on a level ground.

Statement-2: The magnitude of frictional force depends on the nature of the two surfaces in contact.

Given in the figure are two blocks $A$ and $B$ of weight $20 \mathrm{N}$ and $100 \mathrm{N}$, respectively. These are being pressed against a wall by a force $F$ as shown. If the coefficient of friction between the blocks is $0.1$ and between block $B$ and the wall is $0.15$, the frictional force applied by the wall on block $B$ is (assume system in equilibrium):

Two masses $m_1=5 \mathrm{kg}$ and $m_2=10 \mathrm{kg}$ connected by an inextensible string over a frictionless pulley are moving as shown in the figure. The coefficient of friction of horizontal surface is $0.15$. The minimum weight $m$ that should be put on top of $m_2$ to stop the motion is:

In the situation shown in figure, for what value of minimum horizontal force $F$ (in Newton), sliding between middle and lower block will start ? (Take $g=10 \mathrm{m} {\mathrm{s}}^{-2}$)