A stone thrown horizontally from the top of a 18-m tower hits the ground at a point 18 m from the base of the tower. (Ignore any effects due to air resistance.)

Question

(a) Find the speed at which the stone was thrown.
m/s

(b) Find the speed of the stone just before it hits the ground.
m/s

Answer 1

a. h = 0.5g*T^2
h = 18 m.
g = 9.8 m/s^2
T = Fall time in s.
Solve for T.

d = Xo*T
d = 18 m.
Xo = hor. speed in m/s.
T = Time calculated in part a.
Solve for Xo.

b. Y^2 = Yo + 2g*h
Y = Ver. component of Speed just before it hits the gnd.
Yo = 0 = Ver. component of initial speed.
g = 9.8 m/s^2
h = 18 m.
Solve for Y.

V = Sqrt(Xo^2 + Y^2) = Velocity just before it hits the gnd.