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

$A$ block of mass $m$ moving with a velocity $v_0$ on a smooth horizontal surface strikes and compresses a spring of stiffness $k$ until the mass comes to rest,as shown in the figure. This phenomenon is observed by two observers:
$A$: standing on the horizontal surface
$B$: standing on the block
To an observer $B$,when the block is compressing the spring:

In a lift moving up with an acceleration of $5 \,m/s^2$, a ball is dropped from a height of $1.25 \,m$. The time taken by the ball to reach the floor of the lift is ... (nearly) $(g=10 \,m/s^2)$ (in $\,s$)

$A$ child stands on a weighing machine inside a lift. When the lift is going down with acceleration $\frac{g}{3}$,the machine shows a reading $20 \ N$. When the lift goes upwards with acceleration $\frac{g}{3}$,the reading would be ($g=$ gravitational acceleration). (in $N$)

$A$ man of weight $W$ is standing on a lift which is moving downward with an acceleration $a$. The apparent weight of the man is

$A$ box of mass $m \, kg$ is placed on the rear side of an open truck accelerating at $4 \, m/s^2$. The coefficient of friction between the box and the surface below it is $0.4$. The net acceleration of the box with respect to the truck is zero. The value of $m$ is :- $[g = 10 \, m/s^2]$