Acatapult is tested by roman legionnaires. they tabulate the results in a papyrus and 2000 years later the archaeological team reads (distances translated into modern units): range = 0.4 km; angle of launch = π/5 rad; landing height = launch height. what is the initial velocity of launch of the boulders if air resistance is negligible?

64.2 m/s

Explanation:

In the x direction:

x = x₀ + v₀ₓ t + ½ at²

400 m = 0 m + v₀ cos (π/5) t + ½ (0 m/s²) t²

t = 400 / (v₀ cos (π/5))

In the y direction:

y = y₀ + v₀ᵧ t + ½ gt²

0 m = 0 m + v₀ sin (π/5) t + ½ (-9.8 m/s²) t²

0 = v₀ sin (π/5) - 4.9 t

t = v₀ sin (π/5) / 4.9

Therefore:

400 / (v₀ cos (π/5)) = v₀ sin (π/5) / 4.9

1960 = v₀² sin (π/5) cos(π/5)

1960 = ½ v₀² sin(2π/5)

3920 / sin(2π/5) = v₀²

v₀ = 64.2 m/s