Question

The trajectory of a projectile projected from origin is given by the equation y = x − $\frac{2x^2}{5}$ . The initial velocity of the projectile is

• A. $25\, ms^{−1}$
• B. $\frac{2}{5} ms^{−1}$
• C. $\frac{5}{2} ms^{−1}$
• D. $5 ms^{−1}$

Answer 1

Answer: (D)

$y=x -\frac{2x^{2}}{5}$
$tan \, \theta=1$
$\theta=45^{\circ}$
$\frac{g}{2u ^{2} cos ^{2}\theta}=\frac{2}{5}$
$\frac{10}{2u^{2} \frac{1}{2}}=\frac{2}{5}$
$u^{2}=\frac{50}{2}=25$
$u=5 \, ms^{-1}$