(A) – 20 = 15t – 5t²
t = – 1, t = 4
(B) 0 = 15t – 5t²
0 = 15t – 5t²
0 = 5t (3 + t) = 0
t = 3
(C) v_y² = (15)² + 2 × 10 × 20
v_y = (625)1/2 = 25
${\mathrm{v}}_{\mathrm{x}}=15\times \sqrt{3}$
$\mathrm{tamp}\mathrm{\beta }={\mathrm{v}}_{\mathrm{y}}/{\mathrm{v}}_{\mathrm{x}}=\frac{25}{15\times \sqrt{3}}-\frac{5}{3\sqrt{3}}\times \frac{\sqrt{3}}{\sqrt{3}}$
$\mathrm{tamp}\mathrm{\beta }=\frac{5\sqrt{3}}{9}$
$\mathrm{\beta }={\tan }^{-1}\left(\frac{5\sqrt{3}}{9}\right)$
(D) x = v_n × t
$\mathrm{y}=15\sqrt{3}\times 4=60\sqrt{3}\mathrm{m}$