Correct answer is : 7
\(v = \omega \sqrt {A^2-x^2}\)
at \(x = \frac {2A}{3}\)
\(v=\omega \sqrt{A^2- \left(\frac {2A}{3}\right)^2}= \frac {\sqrt 5A\omega}{3}\)
New amplitude = A'
\(v'= 3v = \sqrt {5}A \omega =\omega \sqrt {(A')^2 - \left(\frac {2A}{3}\right)^2}\)
\(A'= \frac {7A}{3}\)
