In the figure,the reading of the spring balance will be $......\,N$ $\left[ g = 10\,m/s^2 \right]$.

$A$ trolley is accelerating down an incline of angle $\theta$ with acceleration $g \sin \theta$. Which of the following is correct? ($\alpha$ is the constant angle made by the string with the vertical.)

$A$ wooden wedge of mass $M$ and inclination angle $\alpha$ rests on a smooth floor. $A$ block of mass $m$ is kept on the wedge. $A$ force $F$ is applied on the wedge as shown in the figure such that the block remains stationary with respect to the wedge. The magnitude of the force $F$ is:

$A$ body of mass $2 \, kg$ is hung on a spring balance mounted vertically in a lift. If the lift descends with an acceleration equal to the acceleration due to gravity $g$,and if the lift moves up with a constant velocity of $2 \, m/s$,the reading on the balance will be ......... $kg$.

An elevator car whose floor-to-ceiling distance is $2.7\,m$ starts ascending with a constant acceleration of $1.2\,m/s^2$. After $2\,s$ of the start,a bolt falls from the ceiling of the car. The free fall time of the bolt is $(g=9.8\,m/s^2)$.

$A$ simple pendulum is attached to a block which slides without friction down an inclined plane $ABC$ having an angle of inclination $\alpha$ as shown below. While the block is sliding down,the pendulum oscillates in such a way that at its mean position,the direction of the string is