A block of mass $m$ moving with a velocity $v_0$ collides with a stationary block of mass $\mathrm{M}$ to which a spring of stiffness $k$ is attached, as shown in figure. Choose the correct alternative(s). 

Consider a block of mass $10 \mathrm{kg}.$ which rests on a smooth surface and is subjected to a horizontal force of $6 \mathrm{N}.$ If observer $A$ is in a fixed frame $x.$

Two blocks of masses $m$ and $M$ are interconnected by an ideal spring of stiffness constant $k$. If $m$ is pushed with a velocity $v_0$, then:

A block of mass $\mathrm{m}$ is placed gently onto a long plank of mass $\mathrm{m}$ moving with a velcoity $v_0$ on a smooth horizontal floor. If friction is present between $M$ and $\mathrm{m}$ :

Consider a hollow sphere of mass $M$ and radius $R$ resting on a smooth surface. A smaller sphere of mass $\mathrm{m}$ and radius $r$ is initially held at position $P$ within the bigger sphere. If the small sphere is now released, it rolls down the inner surface of hollow sphere and finally stops at its bottom point $Q.$ Then:

A long plank$\text{'}A\text{'}$ is at rest on a smooth horizontal surface. A small block ' $B$ ', whose mass is half of ' $A$ ', is placed on the plank at one end and projected along $A$ with some velocity $u.$ The coefficient of friction between the plank and block is $\mu$ :

A uniform wire frame $ABC$ is in the shape of an equilateral triangle in $xy$ -plane with centroid at the origin.