Projectile Motion

Question

A cannon is launched off a 27 m high cliff with an initial velocity of 64.7 m/s and at an angle of 30^o above the horizontal. Find the time of flight.

Answer 1

Use kinematic equation Δy = v_o t + 1/2 a t², -27 = 64.7 sin 30° + 1/2 (-9.8) t² = 32.3₅ - 4.9 t², 4.9 t² - 32.3₅ t -27 = 0, t = {32.3₅ ± [32.35² - 4(4.9)(-27)]^1/2} / 9.8, choose positive root for t = 7.35 sec.