The equation of trajectory of a particle is $x=\sqrt{3}y-5y^2$. The particle is at origin at $t=0$. Its acceleration is $\mathrm{a}=-10\mathrm{i}$. Its initial speed is 

$$\begin{gathered} y-y_0=u_{y}t \\ \text{ or } y-0=u_{y}t \\ \text{ or }y=u_{y}t \\ \text{ and }x-x_0=u_{x}t+\frac{1}{2}{a}_x{t}^2 \\ \text{ or }x-0=u_x\times \frac{y}{u_y}-\frac{1}{2}\times 10\times {\left(\frac{y}{u_y}\right)}^2 \\ \text{ or } x=\frac{u_x}{u_y}y-\frac{5}{u_y^2}{y}^2 \\ \text{ or }\sqrt{3}y-5y^2=\frac{u_x}{u_y}y-\frac{5}{u_y^2}{y}^2 \\ \text{ or }\frac{u_x}{u_y}=\sqrt{3} \\ \text{ and }5=\frac{5}{u_Y^2} \\ {u}_y=1 \\ {u}_x=\sqrt{3}{u}_y=\sqrt{3} \\ u=\sqrt{u_x^2+u_y^2}=2{ \mathrm{ms}}^{-1} \end{gathered}$$