In a vacuum, a projectile launched with initial velocity components has accelerations a_x and a_y. What are they?

In a vacuum, a projectile launched with initial velocity components has accelerations a_x and a_y. What are they?

• A. a_x = g, a_y = 0
• B. a_x = 0, a_y = −g
• C. a_x = −g, a_y = 0
• D. a_x = 0, a_y = −g

Answer: (D)

In projectile motion with no air resistance, gravity is the only force acting on the projectile, and it pulls straight downward. That means there is no horizontal force, so the horizontal acceleration is zero. The vertical acceleration is downward and equals -g (taking up as positive). Therefore, a_x = 0 and a_y = -g. This also explains why the horizontal velocity remains constant while the vertical velocity changes linearly due to the constant downward acceleration.

In projectile motion with no air resistance, gravity is the only force acting on the projectile, and it pulls straight downward. That means there is no horizontal force, so the horizontal acceleration is zero. The vertical acceleration is downward and equals -g (taking up as positive). Therefore, a_x = 0 and a_y = -g. This also explains why the horizontal velocity remains constant while the vertical velocity changes linearly due to the constant downward acceleration.