Use the button to start the action. After, press it again to reset the balls. Use the line to confirm to heights are equal.
In basic kinematics, we learn that the horizontal motion of a projectile will not influence its vertical motion. So, if one ball is just let go (i.e. dropped) and the other is given an initial horizontal velocity (thrown) at the same time, their vertical motions will be identical. At every instant in time, they will be at the same y position.
Link to stand-alone sim: Here is a link to view the sim on its own, with no distractions.