Two identical spring are attached to a small block `P` The other ends of the springs are fixed at A and B. when `P` is equilibrium the extension of top spring is `20cm` and extension of bottom spring is `10cm` The period at small vertical oscillation of `p` about its equilibrium position is (use `g = 9.8m//s^(2))`

Options

A. `(2pi)/(7)sec`
B. `(pi)/(7)sec`
C. `(2pi)/(5)sec`
D. none of these

Answer

B

Explanation

`Mg = K xx 20 - K xx 10 rArr K = (mg)/(10//100) N//m`

`T = 2 pi sqrt((M)/(K))`
`T = 2pi sqrt((1)/(49 xx 4)) = (pi)/(7) sec`