$A$ $10\, kg$ block is placed on a horizontal surface as shown. If an external horizontal force $F = 50\, N$ is applied,find the friction force acting on the block. (Take $g = 10\, m/s^2$)

$A$ box of mass $15 \text{ kg}$ is kept on the floor of a stationary trolley. The coefficient of static friction between the box and the trolley is $0.12$. Keeping the box in a stationary state over the trolley, the maximum acceleration with which the trolley can be moved horizontally in $\text{m s}^{-2}$ is: $(g = 10 \text{m s}^{-2})$

$A$ person initially at rest starts walking towards the east without slipping or skidding. What is the type of friction acting on the person from the ground, and in which direction does the frictional force act?

If the mass of block $A = 10\,kg$,the coefficient of static friction $\mu_s = 0.2$,and the coefficient of kinetic friction $\mu_k = 0.2$,find the mass of block $B$ required to start the motion.

$A$ heavy body of mass $25 \ kg$ is to be dragged along a horizontal plane $\left( \mu = \frac{1}{\sqrt{3}} \right)$. The least force required is ........ $kgf$.

$A$ force of $19.6\, N$ when applied parallel to the surface just moves a body of mass $10\, kg$ kept on a horizontal surface. If a $5\, kg$ mass is kept on the first mass,the force applied parallel to the surface to just move the combined body is........ $N.$