The minimum acceleration with which a fireman can slide down a rope of breaking strength two-third of his weight 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 $m$.

$A$ block of mass $M$ is kept on a platform which starts accelerating upwards from rest with a constant acceleration $a$. During the time interval $T$,the work done by the contact force on mass $M$ is

$A$ horizontal force of $10 \,N$ is applied to a block $A$ as shown in the figure. The masses of blocks $A$ and $B$ are $2 \,kg$ and $3 \,kg$ respectively. The blocks slide over a frictionless surface. The force exerted by block $A$ on block $B$ is:

$A$ block of mass $18.5 \ kg$ kept on a smooth horizontal surface is pulled by a rope of $3 \ m$ length by a horizontal force of $40 \ N$ applied to the other end of the rope. If the linear density of the rope is $0.5 \ kg \ m^{-1}$ and initially the block is at rest,the time in which the block moves a distance of $9 \ m$ is: (in $s$)

The figure shows two blocks connected by a light inextensible string. $A$ force of $10 \,N$ is applied on the bigger block at $60^{\circ}$ with the horizontal. The tension in the string connecting the two masses is ....... $N$.