Click Play to start the simulation. Enter the time when you think those two particle have the same HORIZONTAL speed. (Enter into the text field and the answer will be shown).
You can change the initial velocity for both particle with your mouse (drag the RED arrow).
The horizontal velocity for the top one should be larger than the lower one.
The top one will move with constant velocity, while the second will need to move up the hill (with constant deceleration a=-g*sin?)
You can also drag the yellow box to change the height of the slope.
Two traces shows X(t) for both particles. Try to find out the answer from those two curves.