A Levels Physics (9702)•9702/13/M/J/20

Explanation
Independence of horizontal and vertical motion in projectile motion
Steps:
- Both balls fall from the same height with zero initial vertical velocity, so vertical motion is identical: time to ground , same for both.
- Horizontal velocity is constant (no air resistance): first ball at 20 m/s, second at 10 m/s.
- Horizontal distance = velocity × time, so first ball travels , second : distances different.
- Landing times are the same due to matching vertical fall.
Why C is correct:
- Vertical motion determines time identically; horizontal motion determines distance proportionally to initial speed (projectile motion independence).
Why the others are wrong:
- A: Distances differ due to different horizontal speeds.
- B: Times are the same from identical vertical drops.
- D: Times are the same, not different.
Final answer: C
Topic: Equations of motion
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