"When a man walks on a rough surface,the frictional force acts in the direction opposite to his motion." Is this statement correct? Give reasons.

$A$ body of mass $40\,kg$ resting on a rough horizontal surface is subjected to a force $P$ which is just enough to start the motion of the body. If $\mu_{s} = 0.5$,$\mu_{k} = 0.4$,$g = 10\,m/s^2$,and the force $P$ is continuously applied on the body,then the acceleration of the body is $.........\,m/s^2$.

$A$ block is thrown with a velocity of $2 \, m/s$ (relative to the ground) on a belt,which is moving with a velocity of $4 \, m/s$ in the opposite direction of the initial velocity of the block. If the block stops slipping on the belt after $4 \, s$ of throwing,then choose the correct statement$(s)$:

$A$ uniform chain of length $L$ is lying on a horizontal table. If the coefficient of friction between the chain and the table top is $\mu$,what is the maximum length of the chain that can hang over the edge of the table without disturbing the rest of the chain on the table?

Consider a car moving along a straight horizontal road with a speed of $72 \, km/h$. If the coefficient of kinetic friction between the tyres and the road is $0.5$,the shortest distance in which the car can be stopped is ........ $m$. $[g = 10 \, m/s^2]$

$A$ block of mass $5 \, kg$ lies on a rough horizontal table. $A$ force of $19.6 \, N$ is enough to keep the body sliding at uniform velocity. The coefficient of sliding friction is