The spring is initially in unstretched condition. It is first stretched by a length '$x$' and the work done is $W_1$. Then again it is stretched by further length '$x$' when the work done is $W_2$. The value of $W_2$ is given by

A body of mass 1kg begins to move under the action of a time dependent force $\vec{F} = (t\hat{i} + 3t^2\hat{j})\ \text{N}$ where $\hat{i}$ and $\hat{j}$ are the unit vectors along x and y axis. The power developed by the above force at time $t = 2\ \text{s}$ will be (in watt)

A block of mass 'm' moving on a frictionless horizontal surface collides with a spring of spring constant 'K' and compresses it through a distance 'x'. The maximum momentum of the block after collision is