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 ............. $\mathrm{J}$

Two masses $m_1 = 2\,kg$ and $m_2 = 5\,kg$ are moving on a frictionless surface with velocities $10\,m/s$ and $3\,m/s$ respectively. An ideal spring is attached on the back of $m_2$ . The maximum compression of the spring will be ............... $\mathrm{m}$

Give the example of variable force. Write the formula of Hook’s law.

A ball of mass $4\, kg$, moving with a velocity of $10\, ms ^{-1}$, collides with a spring of length $8\, m$ and force constant $100\, Nm ^{-1}$. The length of the compressed spring is $x\, m$. The value of $x$, to the nearest integer, is ........ .

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

Two plates each of mass $m$ are connected by a massless spring as shown below. A weight $w$ is put on the upper plate which compresses the spring further. When $w$ is removed, the entire assembly jumps up. The minimum weight $w$ needed for the assembly to jump up when the weight is removed is just more than ...........$ \,m$