Two identical balls collide<span> head on. The </span>initial velocity<span> of </span>one<span> is 0.75 </span>m/s<span> east, while that of the </span>other one<span> is 0.43 </span>m/s west<span>.</span>
First off, you need to know the weight of the projectile, lift and drag coefficients something like a high Reynolds number is preferred, then use the gravitational constant of 9.8 meters per second squared those would be a good start to get closer to your goal
Make the base of the building zero. Then the initial distance is 100m, final distance unknown x. Use gravity, time and initial velocity to solve for final distance.
x - 100 = (0)(5) +(1/2)(-9.81)(5^2)
x - 100 = 0 - 122.625
x = -122.625 + 100
x = -22.625 m below ground