As per the question the paper air plane is launched horizontally.

The initial speed of the paper air plane is 2.3 m/s.

As the paper air plane is not consuming any type of fuel,so it is considered as a projectile.We know that  projectile motion is always under gravity.Here the paper air plane is fired horizontally .Hence the trajectory of the projectile will be parabolic.

Initially the vertical velocity of the projectile is zero and horizontal velocity is 2.3 m/s.

The horizontal velocity is always a constant quantity. Hence there is no acceleration in horizontal direction. Due to the horizontal component the particle will move horizontal distance.

As the gravity pulls the body downward,finally the plane will fall on the ground.Let the air resistance for the projectile is very small and it is neglected.Hence the only force that acts on the plane is the force of gravity.Hence every time the vertical velocity of the plane increases at a rate of 9.8 m/s.Hence the acceleration produced due to the vertical component of the projectile is 9.8 m/s^2 which is acceleration due to gravity.

The instantaneous velocity at any time is given as-

                                                v= u+at

                                                v_{y} =0+[-g]t [ here u and v are the initial and final velocity]

                                                v_{y} = -gt

Here g is taken negative for vertically downward motion.