Question

a small rock is thrown with a speed of 20m/s and at an angle of 37 degrees above the horizontal from the roof of a tall building. the rock strikes the grounda distance of 80 m from the base of the building. air resistance can be neglected

a)what is the height of the building

b)what is the speed of the rock just before it strikes the ground?

please show the kinematic equations used

Answer 1

a) s = ut + 1/2 at^2 h = u_y t + 1/2 a_y t^2 -h = u_y t - 1/2 gt^2 and R = U_x t Rightarow 80 = u cos theta times t Rightarow 80 = 20 cos 37 degree times t Rightarow t = 5.0 s therefore - h = u sin theta times t - 1/2 gt^2 + h = -20 sin 37 times 5 + 1/2 times 9.8 times (5)^2 = 62.3 m \r\nb) v_y = u_y - gt = u sin theta - gt = 20 sin 37 - 9.8 times 5 = -36 .96 m/s v = squareroot v^2_x + v^2_y = squareroot u_x^2 + v^2_y = squareroot (u cos theta)^2 + v_y^2 = squareroot (20 cos 37)^2 + (36.96)^2 = 40.26 m/s