$A$ disc of mass $100 \,g$ slides down from rest on an inclined plane of $30^{\circ}$ and comes to rest after travelling a distance of $1 \,m$ along the horizontal plane. If the coefficient of friction is $0.2$ for both inclined and horizontal planes, then the work done by the frictional force over the whole journey, approximately, is (Acceleration due to gravity, $g=10 \,ms^{-2}$) (in $\,J$)

Imagine the situation in which the given arrangement is placed inside a trolley that can move only in the horizontal direction,as shown in the figure. If the trolley is accelerated horizontally along the positive $x$-axis with $a_0$,then identify the correct statement$(s)$ related to the tension $T$ in the string.

In the figure,a block of weight $60 \, N$ is placed on a rough surface. The coefficient of friction between the block and the surface is $0.5$. Find the maximum weight $W$ such that the block does not slip on the surface.

Write the advantages and disadvantages of friction. Write the remedies to reduce friction.

In the arrangement shown in the figure,the masses of blocks $B$ and $A$ are $2m$ and $m$ respectively. The surface between $B$ and the floor is smooth. Block $B$ is connected to block $C$ by means of a string-pulley system. If the whole system is released,find the minimum value of the mass of block $C$ so that block $A$ remains stationary with respect to $B$. The coefficient of friction between $A$ and $B$ is $\mu$.

$A$ $1 \,kg$ block situated on a rough incline is connected to a spring of negligible mass having spring constant $100 \,N \,m^{-1}$ as shown in the figure. The block is released from rest with the spring in the unstretched position. The block moves $10 \,cm$ down the incline before coming to rest. The coefficient of friction between the block and the incline is (Take $g=10 \,m \,s^{-2}$ and assume that the pulley is frictionless).