Horizontal velocity constant; vertical accelerates linearly

Steps:

• Object projected horizontally: initial vertical velocity is zero, horizontal velocity constant (no horizontal forces).
• Uniform gravity: vertical acceleration g downward, so vertical velocity v_y = gt (linear increase if downward positive).
• Horizontal velocity v_x remains constant, so graph is horizontal straight line.
• Match graphs: Q shows constant velocity (horizontal line) for v_x; P shows linearly increasing velocity for v_y.

Why A is correct:

• Newton's first law: no horizontal acceleration, so v_x constant (Q); second law: constant g gives linear v_y (P, from v = u + at with u=0).

Why the others are wrong:

• B: S likely curved or incorrect slope, not linear for constant g.
• C: R probably not constant, violates no horizontal acceleration.
• D: R not constant and S not linear, both mismatch projectile motion.

Final answer: A