$A$ balloon of mass $M$ descends with an acceleration $a (< g)$. What mass needs to be removed from the balloon so that it starts ascending with acceleration $a$?

$A$ body of mass $M$ tied to a string is lowered at a constant acceleration of $(g/4)$ through a vertical distance $h$. The work done by the string will be..............

$A$ constant horizontal force $\overrightarrow{F}$ of magnitude $10 \,N$ is applied to a block $A$ and this produces an acceleration of magnitude $20 \,m/s^2$. If this block $A$ is then kept against another block $B$ of mass $1.5 \,kg$ as shown in the figure and a force $F^{\prime}$ of $20 \,N$ is applied,find the force on the block $B$. Neglect friction. (in $N$)

$A$ monkey is descending from the branch of a tree with constant acceleration. If the breaking strength of the branch is $75 \%$ of the weight of the monkey,what is the minimum acceleration with which the monkey can slide down without breaking the branch?

$A$ mass $1\, kg$ is suspended by a thread. It is
$(i)$ lifted up with an acceleration $4.9\, m/s^2$
$(ii)$ lowered with an acceleration $4.9\, m/s^2$.
The ratio of the tensions is

$A$ block of mass $m$ is connected to another block of mass $M$ by a massless spring of spring constant $k$. The blocks are kept on a smooth horizontal plane. Initially,the blocks are at rest and the spring is unstretched. Then a constant force $F$ starts acting on the block of mass $M$ to pull it. Find the force acting on the block of mass $m$.