If the initial velocity in horizontal direction of a projectile is...

Given here, initial velocity, ${u}_{x} = 1$

Equation of trajectory, $y = 5x\left(1 - x\right) = 5x - 5{x}^{2}$

Now, differentiating the above equation,

$\dfrac{d y}{d t} = 5\dfrac{d x}{d t} - 10x\dfrac{d x}{d t}$

For initial $y$-component of velocity

${u}_{y} = {\left(\dfrac{d y}{d t}\right)}_{x = 0} ⇒ 5\left(1\right) = 5$

\overset{\to}{u}y = 5\overset{^}{j}