$A$ block of mass $m$ is hung vertically from an elastic thread of force constant $\frac{2mg}{a}$. Initially,the thread is at its natural length and the block is allowed to fall freely. The work done on the block by the Earth when it passes through the equilibrium position will be:

The potential energy of a long spring when stretched by $2\,cm$ is $U$. If the spring is stretched by $8\,cm$,the potential energy stored in it will be $.......\,U$.

When a body of mass $m$ is attached to a vertical spring of natural length $L$ and released,the spring stretches by a distance $h$. What will be the potential energy of the stretched spring?

$A$ spring with spring constant $k$ is extended from $x = 0$ to $x = x_1$. The work done will be

$A$ massless platform is kept on a light elastic spring as shown in the figure. When a sand particle of mass $0.1 \; kg$ is dropped on the pan from a height of $0.24 \; m$,the particle strikes the pan and the spring is compressed by $0.01 \; m$. From what height should the particle be dropped to cause a compression of $0.04 \; m$ (in $; m$)?