$A$ 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

Find the work done against friction in $J$ when a block of mass $50\, kg$ moves a distance of $1\, m$ on a rough horizontal surface with a coefficient of friction of $0.2$.

$A$ block is kept on a rough horizontal surface. The acceleration of the block increases from $6 \ m/s^2$ to $11 \ m/s^2$ when the horizontal force acting on it increases from $20 \ N$ to $30 \ N$. The coefficient of kinetic friction between the block and the surface is (Acceleration due to gravity $g = 10 \ m/s^2$):

$A$ body of mass $2 \, kg$ moving on a horizontal surface with an initial velocity of $4 \, m/s$ comes to rest after $2 \, s$. If one wants to keep this body moving on the same surface with a constant velocity of $4 \, m/s$,the force required is ........ $N$.

"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.

What is the maximum value of the force $F$ such that the block shown in the arrangement does not move (in $N$)? (Given $m = \sqrt{3} \ kg$,$\mu = \frac{1}{2\sqrt{3}}$,$g = 10 \ m/s^2$)