Answer:
[tex]\frac{t_1}{t_2} = \frac{sin\theta_1}{sin\theta_2}[/tex]
Explanation:
The vertical component of the initial velocities are
[tex]v_v = v_0sin\theta[/tex]
If we ignore air resistance, and let g = -9.81 m/s2. The the time it takes for the projectiles to travel, vertically speaking, can be calculated in the following motion equation
[tex]v_vt - gt^2/2 = s = 0[/tex]
[tex]t(v_v - gt/2) = 0[/tex]
[tex]v_v - gt/2 = 0[/tex]
[tex]t = 2v_v/g = 2v_0sin\theta/g[/tex]
So the ratio of the times of the flights is
[tex]t_1 / t_2 = \frac{2v_0sin\theta_1/g}{2v_0sin\theta_2/g} = \frac{sin\theta_1}{sin\theta_2}[/tex]