$A$ block of mass $m$ is pulled by a force of $40 \, N$ on a smooth horizontal surface as shown in the figure. The tension at the middle of the block is ........... $N$.

Two weights $W_1$ and $W_2$ are tied to a massless string and passed over a pulley. If the pulley is accelerated upwards with an acceleration $g$,what will be the tension in the string?

In order to raise a mass of $100\,kg$,a man of mass $60\,kg$ fastens a rope to it and passes the rope over a smooth pulley. He climbs the rope with an acceleration $5g/4$ relative to the rope. The tension in the rope is ....... $N$. $(g = 10\,m/s^2)$

$A$ block of mass $M$ is hanging over a smooth and light pulley through a light string. The other end of the string is pulled by a constant force $F$. The kinetic energy of the block increases by $20\,J$ in $1\,s$.

For the given system,the acceleration of the system is ........... $m/s^2$.

The pulley arrangements shown in the figure are identical, and the mass of the rope is negligible. In case $I$, the mass $m$ is lifted by attaching a mass $2m$ to the other end of the rope. In case $II$, the mass $m$ is lifted by pulling the other end of the rope with a constant downward force $F = 2mg$, where $g$ is the acceleration due to gravity. The acceleration of mass $m$ in case $I$ is