Q: An ideal spring with spring-constant k is hung from the ceiling and a block of mass M is attached to its lower end. The mass is released with the spring initially unstretched. Then the maximum extension in the spring is
(a)$\displaystyle \frac{4 M g}{k}$
(b) $\displaystyle \frac{2 M g}{k}$
(c) $\displaystyle \frac{ M g}{k}$
(d) $\displaystyle \frac{ M g}{2 k}$
Ans: (b)
$\displaystyle M g x = \frac{1}{2} k x^2 $
$\displaystyle x = \frac{2 M g}{k}$