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 $k = 2\,N/s^2$. Coefficient of friction $\mu = 0.8$. Force of friction between block and the plane at $t = 2\,s$ is ....... $N$
$8$
$4$
$2$
$32$
In the figure shown, horizontal force $F_1$ is applied on a block but the block does not slide. Then as the magnitude of vertical force $F_2$ is increased from zero the block begins to slide; the correct statement is
A block of mass $m$ is pressed against a vertical surface by a spring of unstretched length $l$ . If the coefficient of friction between the block and the surface is $\mu $. Choose the correct statement.
A girl holds a book of mass $m$ against a vertical wall with a horizontal force $F$ using her finger, so that the book does not move. The frictional force on the book by the wall is
A block of mass $m$ is placed on a surface having vertical cross section given by $y=x^2 / 4$. If coefficient of friction is $0.5$ , the maximum height above the ground at which block can be placed without slipping is:
A horizontal force $12 \,N$ pushes a block weighing $1/2\, kg$ against a vertical wall. The coefficient of static friction between the wall and the block is $0.5$ and the coefficient of kinetic friction is $0.35.$ Assuming that the block is not moving initially. Which one of the following choices is correct (Take $g = 10 \,m/s^2$)