On the horizontal surface of a truck,a block of mass $1 \; kg$ is placed $(\mu = 0.6)$. If the truck is moving with an acceleration of $5 \; m/s^2$,then the frictional force on the block will be: (in $; N$)

One end of a spring of force constant $150 \text{ dyne cm}^{-1}$ is connected to a block of mass $0.2 \text{ kg}$ kept on a rough horizontal surface of coefficient of friction $0.3$. The other end of the spring is connected to a rigid support as shown in the figure and the spring is initially undeformed. The maximum velocity $v$ that can be given to the block so that it travels only in one direction is . . . . . . $\text{ms}^{-1}$. (Acceleration due to gravity $= 10 \text{ ms}^{-2}$)

Match the items in Column-$I$ with those in Column-$II$.

Column-$I$	Column-$II$
$(1)$ Definition of force	$(a)$ Newton's third law of motion
$(2)$ Measurement of force	$(b)$ Newton's second law of motion
	$(c)$ Newton's first law of motion

Two wedges each of mass $600 \ g$ are placed next to each other on a rough horizontal surface. The coefficient of static friction between the wedges and the surface is $0.4$. $A$ cube of mass $M$ is balanced on the wedges as shown in the figure. If there is no friction between the cube and wedges,the largest mass $M$ of the cube that can be balanced without motion of the wedges is . . . . . . $kg$.

Shown in the diagram is a system of two bodies,a block of mass $m$ and a disc of mass $4m$,held in equilibrium. If the string $3$ is burnt,find the acceleration of the disc. Neglect the masses of the pulleys $P$ and $Q$. The coefficient of friction between the block and the horizontal surface is $0.5$ and the friction between the disc and the string is zero. (Take $g = 10 \ m/s^2$)

Which of the following is not a fundamental force in nature?