A block of mass `1 Kg` is fastened to one each of a wire of cross-sectional area of `2mm^(2)` and is rotated in verticle circle of radius `20cm`. The speed of the block at the bottom of the circle is `3.5ms^(-1)`. The elongation of the wire when the block is at top of the circle

Options

A. `0.6125xx10^(-5)m`
B. `0.6125xx10^(-4)m`
C. `0.6125xx10^(-3)m`
D. `0.6125xx10^(-2)m`

Answer

A

Explanation

(i) Tension at the bottom of the circle,
`T = (mv^(2))/(r) + mg, e = (Fl)/(AY)`
(ii) Tension at the top of the circle,
`T` = Tension at the bottom `-6mg`
The increment in lengh `e = (Fl)/(AY)`