A cannon is fired at an angle of 30 degrees above the horizontal from a cliff th

Question

A cannon is fired at an angle of 30 degrees above the horizontal from a cliff that is 20m above a flat river bottom. What is the initial speed of the projectile if it is found to land 40m from the base of the cliff?

Please include relevant explanations as well! Thanks a lot! :D

Explanation / Answer

Vi = initial speed g = 9.8 m/s² x = (Vicos30)t ==>40 = (Vicos30)t ==> t = 40/(Vicos30) y = 20 + (Visin30)t - gt²/2 ------------ 0 = 20 + (Visin30)40/(vicos30) - 9.8(40/(Vicos30))²/2 0 = 20 + 40tan30 - 7840/(Vicos30)² Vi = 15.57m/s ==> answer # the vertical distance y = 0 because the horizontal distance 40 m is obtained at the river level ==> y = 0

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