Two blocks $A$ and $B$ of masses $5 \ kg$ and $10 \ kg$ respectively are placed as shown in the figure. The coefficient of friction between all the surfaces is $0.2$. $A$ force $F$ is applied on block $A$ at an angle of $30^{\circ}$ with the horizontal. If the system moves with constant acceleration,find the acceleration of block $B$. (Assume $g = 10 \ m/s^2$ and $F = 100 \ N$) (in $m/s^2$)

$A$ bird is sitting in a large closed cage which is placed on a spring balance. It records a weight of $25 \, N$. The bird (mass $m = 0.5 \, kg$) flies upward in the cage with an acceleration of $2 \, m/s^2$. The spring balance will now record a weight of ........ $N$.

Assertion $(A):$ Two identical trains move in opposite senses in the equatorial plane with the same speeds relative to the Earth's surface. They have equal magnitude of normal reaction.
Reason $(R):$ The trains have different centripetal accelerations due to different speeds.

$A$ force $F = Kt$ (where $t$ is the time in seconds and $K = 2 \, N/s$) is applied on a $2 \, kg$ block at $t = 0$ as shown in the figure. The displacement of the $8 \, kg$ block until the time when the $2 \, kg$ block starts slipping on the $8 \, kg$ block will be (coefficient of friction between the $2 \, kg$ block and the $8 \, kg$ block is $0.2$ and between the $8 \, kg$ block and the surface is zero,$g = 10 \, m/s^2$).

$A$ box '$A$' is lying on the horizontal floor of the compartment of a train running along horizontal rails from left to right. At time '$t$',it decelerates. Then the reaction $R$ by the floor on the box is given best by

$A$ mass of $1 \text{ kg}$ is kept on an inclined plane with $30^\circ$ inclination with respect to the horizontal plane and it is at rest initially. Then, the whole assembly is moved up with a constant velocity of $4 \text{ m/s}$. The work done by the frictional force in time $2 \text{ s}$ is . . . . . . $\text{J}$. (Take $g = 10 \text{ m/s}^2$)