d
\(L ^{2}=x^{2}+y^{2}\)

On differentiating we get,

\(0=2 x \frac{ dx }{ dt }+2 y \frac{ dy }{ dt }\)

The Velocity of \(A =\frac{ dx }{ dt }=-10 m / s\)

The velocity of particle \(B=\frac{ d y}{ dt }\)

\(\frac{ d y}{ dt }=\frac{- x }{ y } \frac{ dx }{ dt }=\cot 60^{0} \times 10=\frac{1}{\sqrt{3}} \times 10=5.8 m / s\)