Question

a projectile is launched at a velocity of 125m/s at an angle of 20 degrees. A building is 200m away. At what height above the ground will the projectile strike the building?

Answer 1

How long to hit the building?
Horizontal problem:
u = 125 cos 20
t = 200/u
the projectile is therefore in the air for t seconds, use that in the vertical problem
Vertical problem:
Vi = 125 sin 20
h = 0 + Vi t - 4.9 t^2

Answer 2

i don't understand the h= 0+Vit-4.9t^2 part where did the 4.9 come from ??