$A$ block of mass $4\,kg$ is placed on a rough horizontal plane. $A$ time-dependent force $F = kt^2$ acts on the block,where $k = 2\,N/s^2$. The coefficient of friction is $\mu = 0.8$. The force of friction between the block and the plane at $t = 2\,s$ is ....... $N$.

Two blocks of masses $M_1$ and $M_2$ are connected with a string passing over a pulley as shown in the figure. The block $M_1$ lies on a horizontal surface. The coefficient of friction between the block $M_1$ and the horizontal surface is $\mu$. What additional mass $m$ should be placed on the block $M_1$ so that the system does not accelerate?

On a rough horizontal surface,a body of mass $2 \, kg$ is given a velocity of $10 \, m/s$. If the coefficient of friction is $0.2$ and $g = 10 \, m/s^2$,the body will stop after covering a distance of ........ $m$.

$A$ horizontal force of $129.4 \, N$ is applied on a $10 \, kg$ block which rests on a horizontal surface. If the coefficient of friction is $0.3$,the acceleration should be ....... $m/s^2$.

$A$ block of mass $5\, kg$ is on a rough horizontal surface and is at rest. Now a force of $24\, N$ is imparted to it with negligible impulse. If the coefficient of kinetic friction is $0.4$ and $g = 9.8\, m/s^2$,then the acceleration of the block is ........ $m/s^2$.

$A$ car is moving on a straight horizontal road with a speed $v.$ If the coefficient of friction between the tyres and the road is $\mu ,$ the shortest distance in which the car can be stopped is