Given in the figure are two blocks $A$ and $B$ of weight $20\ N$ and $100\ N,$ 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 ........... $N$.

$A$ $300\ kg$ crate is dropped vertically onto a conveyor belt that is moving at $1.20\ m/s$. $A$ motor maintains the belt's constant speed. The belt initially slides under the crate,with a coefficient of friction of $0.400$. After a short time,the crate is moving at the speed of the belt. During the period in which the crate is being accelerated,find the work done by the motor which drives the belt :- ................. $J$

Consider the following statements $A$ and $B$ and identify the correct answer:
$A$. When a person walks on a rough surface,the direction of the frictional force exerted by the surface on the person is in the same direction as his motion.
$B$. When a cycle is in motion,the force of friction exerted by the ground on the front wheel is in the backward direction.

Four blocks $A, B, C$ and $D$ of masses $6 \,kg, 3 \,kg, 6 \,kg$ and $1 \,kg$ respectively are connected by light strings passing over frictionless pulleys as shown in the figure. The strings $P$ and $Q$ are horizontal. The coefficient of friction between the horizontal surface and the block $B$ is $0.2$ and the blocks $A$ and $B$ move together. If the system is released from rest, then the tension in the string $Q$ is (Acceleration due to gravity, $g=10 \,ms^{-2}$) (in $\,N$)

At time $t=0$,a force $F=\alpha t$,where $t$ is time in seconds,is applied to a body of mass $1 \text{ kg}$,resting on a smooth horizontal plane. If the direction of the force makes an angle of $45^{\circ}$ with the horizontal,then the velocity of the body at the moment of its breaking off the plane is

$A$ long plank $P$ of mass $5\, kg$ is placed on a smooth floor. On $P$ is placed a block $Q$ of mass $2\, kg$. The coefficient of friction between $P$ and $Q$ is $0.5$. If a horizontal force $15\, N$ is applied to $Q$,as shown,and you may take $g$ as $10\, N/kg$,then which of the following statements is correct?