Radius of the circle, \(r=1.5 \,m\)

Number of revolution per second, \(n=\frac{40}{60}=\frac{2}{3} \,rps\)

Angular velocity, \(\omega=\frac{v}{r}=2 \pi n\)

The centripetal force for the stone is provided by the tension \(T\), in the string, i.e., \(T=F_{\text {Centripetal }}\)

\(=\frac{m v^{2}}{r}=m r \omega^{2}=m r(2 \pi n)^{2}\)

\(=0.25 \times 1.5 \times\left(2 \times 3.14 \times \frac{2}{3}\right)^{2}\)

\(=6.57\, N\)

Maximum tension in the string, \(T_{\max }=200 \,N\)

\(T_{\max }=\frac{m v_{\max }^{2}}{r}\)

\(\therefore v_{\max }=\sqrt{\frac{T_{\max } \times r}{m}}\)

\(=\sqrt{\frac{200 \times 1.5}{0.25}}\)

\(=\sqrt{1200}=34.64 \,m / s\)

Therefore, the maximum speed of the stone is \(34.64 \,m / s\)