A spring $40 \,mm$ long is stretched by the application of a force. If $10 \,N$ force required to stretch the spring through $1 \,mm$, then work done in stretching the spring through $40\, mm$ is …………. $\mathrm{J}$

As shown in figure there is a spring block system. Block of mass $500\,g$ is pressed against a horizontal spring fixed at one end to compress the spring through $5.0\,cm$ . The spring constant is $500\,N/m$ . When released, calculate the distance where it will hit the ground $4\,m$ below the spring ? $(g = 10\,m/s^2)$

Two masses $A$ and $B$ of mass $M$ and $2M$ respectively are connected by a compressed ideal spring. The system is placed on $a$ horizontal frictionless table and given $a$ velocity $u\, \hat k$ in the $z$ -direction as shown in the figure. The spring is then released. In the subsequent motion the line from $B$ to $A$ always points along the $\hat i$ unit vector. At some instant of $\rho$ time mass $B$ has $a$ $x$ -component of velocity as $V_x\, \hat i$ . The velocity ${\vec V_A}$ of as $A$ at that instant is

A block of mass $m = 0.1\,kg$ is connected to a spring of unknown spring constant $k.$ It is compressed to a distance $x$ from its equilibrium. position and released from rest . After approaching half the distance $(\frac {x}{2})$ from equilibrium position, it hits another block and comes to rest momentarily, while the other block moves with a velocity $3\,ms^{-1}.$ The total initial energy of the spring is ……………. $\mathrm{J}$

The work done in joules in increasing the extension of a spring of stiffness $10\, N/cm$ from $4\, cm$ to $6\, cm$ is: