$A$ body is pulled along a rough horizontal surface with a velocity $6\,m/s$. If the body comes to rest after travelling $9\,m$,then the coefficient of sliding friction is- (Take $g = 10\,m/s^2$)

$A$ body of weight $50 \,N$ placed on a horizontal surface is just moved by a force of $28.2 \,N$ applied at an angle of $45^\circ$ with the horizontal. The frictional force and the normal reaction are

$A$ block of $7\,kg$ is placed on a rough horizontal surface and is pulled by a variable force $F$ (in $N$) $= 5t$,where $t$ is time in seconds,at an angle of $37^{\circ}$ with the horizontal as shown in the figure. The coefficient of static friction between the block and the surface is $\mu = 1$. If the force starts acting at $t = 0\,s$,find the time at which the block starts to slide. (Take $g = 10\,m/s^2$)

$A$ block is projected with speed $20 \,m/s$ on a rough horizontal surface. The coefficient of friction $(\mu)$ between the surfaces varies with time $(t)$ as shown in the figure. The speed of the body at the end of $4 \,s$ will be ............ $m/s$ $(g = 10 \,m/s^2)$.

$A$ block of mass $2 \,kg$ is being pushed against a wall by a force $F=90 \,N$ as shown in the figure. If the coefficient of friction is $0.25$, then the magnitude of acceleration of the block is (Take $g=10 \,ms^{-2}$, $\sin 37^{\circ}=\frac{3}{5}$). (in $\,ms^{-2}$)

What is rolling friction? Write the laws of rolling friction. Define the coefficient of rolling friction.