Question

Block is at rest in equilibrium. Now suddenly support is removed so that upper end of spring is only connected with one end of string having length 88 cm, If acceleration of block and tension i string just after removing the support is a and T, then-

• A. a = Zero, T = 14
• B. $a=3m/s^2,T=14$
• C. $a=3m/s^2,T=0$
• D. T = 20 N, a = zero

Answer 1

Answer: (A)

a = Zero, T = 14

$\begin{array}{c}\text{Correct option is (}A\text{)}\\ \text{Initially string is of}85cm\text{and spring}\\ \text{is extended}\\ \begin{array}{cc}kx& =mg\\ 200x& =20\\ x& =10cm\end{array}\end{array}$

$\begin{array}{cc}\text{When support is removed spring goes}& \\ x_0=(88-85)cm\text{down but now also}& \\ 2kg\text{block is in acceleration}=0& \\ \text{Now:}& \\ \begin{array}{cc}T& =k(x-x_0)\\ & =200/100\times (10-3)\end{array}& \\ & =14N\end{array}$