Question

After a projectile is fired into the air, what is the acceleration in the x-direction? (Assume no air resistance.)

Answer 1

Without air resistance, there is no horizontal force on the projectile,
so it has no horizontal acceleration.  The answer is "zero".
 

Answer 2

Answer:

$a_x = 0$

Explanation:

When projectile is in air then the force on the projectile is only due to its weight

It is vertically downwards

$F_g = mg(-\hat j)$

so here since we don't have any air drag or friction due to air so there will be no force along its tangent or along x direction

so the acceleration along x direction will be zero

$a_x = 0$

$a_y = - g$