$\frac{?}{\text{B}\text{a}\text{r}}AB$ is $1$ meter long. When the bar is vertical the spring is unstretched. Calculate the change in length of the spring as well as weight acting downward at the centre of rod $AB.$ Use $\text{'}n\text{'}=$ question number and $=30.$ Ignore the self$-$weight of bar $AB.$ Write the solution step by step. Make sure to present your solutions clearly and legibly. $($example: If question number is $2,n=2)$