physics homework question?

Question

A rock is thrown from a building at 60 degrees it lands 10.3 m away. How tall is the building?answer in m.?
mass-.77kg
vi-8.36
angle-60 degrees
d-10.3
a-9.8 m/s^2
assume: The ground is level and that the side of the building is vertical.

Answer 1

The horizontal motion is described by

x - xo = vox t

x - xo = horizontal distance traveled, 10.3 m
vox = initial horizontal velocity, ( 8.36 m/s ) cos 60
t = elapsed time

Solve for time

The vertical motion is described by

y - yo = voy t - 1/2 g t^2

y - yo = the height of the building
voy = ( 8.36 m / s ) sin 60
g = 9.8 m/s^2
t = elapsed time found in previous part

Solve for the height of the building.

Answer 2

Vx = Vicos60
X = VxT = ViTcos60
T = X/Vicos60
H + Visin60T - (1/2)gT^2 = 0
H + Visin60X/Vicos60 - (1/2)g(X/Vicos60)^2 = 0
H + Xtan60 - (1/2)g(X/Vicos60)^2 = 0
H = (1/2)gX(1/Vicos60)^2 - tan60)
H = (1/2)(9.8)(10.3)(1/8.36cos60)^2 - tan60)
H ≈ 84.5280 m. ≈ 84.5 m.