A stone is thrown from the top of a building upward at an angle of 30.0∘to the horizontal and with an initial speed of 20.0 m/s. If the height of the building is 45.0 m, what is the speed in m/sec of the stone just before it strikes the ground ?

Answer 1

u = 20 cos 30 until it hits the ground.

Vi = initial vertical velocity = +20 sin 30 = +10

initial vertical displacement = 45
final vertical displacement = 0

0 = 45 + Vi t - 4.9 t^2
solve for t

v = Vi - 9.8 t
solve for v

speed = sqrt (u^2 + v^2)