Question

A rocket is projected horizontally with velocity 700meter per seconds from the top of a tower 100meter high. how long will it take to reach the ground?

Answer 1

Let's check this with the time to fall 100m, then doubling that.
0=100-4.9t^2
t= 10 sqrt(1/4.9)=4.52 seconds
remember the 700m/s speed is horizontal