Question

Part A: give an answer and explain it

A particle is projected upwards from the top of a building of height h with a velocity u! = (ux ,uy ), making an angle θ with the horizontal. Ignoring air resistance, the time t taken by the mass to reach the ground is given by

Answer 1

As soon as particle is projected gravitational acceleration starts acting on particle evry time and that of that acceleration is in negative Y direction or downward direction so it starts affecting the the velocity in y direction and velocity will decrease in y direction till it reversed its path in y direction .
But the component of velocity in x direction will never change because there is forece or acceleration in x direction.
After solving the quadratic equation in time(t) we will consider only positive sign because time can never be negative quantity that's why we don't consider minus sign in the roots