Answer:
D. remains constant throughout the fall.
Explanation:
Horizontal Launching
We can launch an object in free air in three forms: vertically, horizontally or inclined. In any case, the only acting force to modify the object's velocity and make it go back to the ground is the force of gravity and it's always directed downwards. Unless friction or air resistance is considered, the horizontal motion is not affected because no force is acting in that direction.
The rock described in the question was launched at 3 m/s pointed horizontally. Immediately after launching, the rock starts to fall to the ground and gain vertical velocity, but the horizontal component remains the same until it completes the flight.
The D option is correct: the horizontal velocity of the rock remains constant throughout the fall
