A wooden block of mass $M$ resting on a rough horizontal floor is pulled with a force $F$ at an angle $\varphi$ with the horizontal. If $\mu$. is the coefficient of kinetic friction between the block and the surface, then the acceleration of the block is
 

Two blocks of masses $0.2 \mathrm{kg}$ and $0.5 \mathrm{kg}$, which are placed $22 \mathrm{m}$ apart on a rough horizontal surface $(\mu =0.5)$, are acted upon by two forces of magnitude $3 \mathrm{N}$ each as shown in figure at time $t=0$. Then, the time $t$ at which they collide with each other is 

Two blocks $m$ and $M$ tied together with an inextensible string are placed at rest on a rough horizontal surface with coefficient of friction $\mu$. The block $m$ is pulled with a variable force $F$ at a varying angle $\theta$ with the horizontal. The value of $\theta$ at which the least value of $F$ is required to move the blocks is given by

In the given figure, the tension in the rope (rope is light) is