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If projectiles $A$ and $B$ are projected horizontally with different initial velocity from the same height, then both $A$ and $B$ possess the same vertical component of velocity, at any instant.

Since the initial velocity is in the horizontal direction, the vertical component at this instant is 0. However, as the particles start falling towards the ground, they get accelerated towards the ground(due to g), and since they have different initial velocities, I cannot understand why their vertical component must be the same.

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  • $\begingroup$ "possess the same vertical component of velocity" when? Initially, or always. acceleration is independent of the material content of the projectile so no matter what, neglecting air resistance, the vertical motion will be the same. But your question is too vague and requires a lot of assuming. $\endgroup$ – ggcg May 13 at 12:07
  • $\begingroup$ It is always. I changed it. $\endgroup$ – Chrys May 13 at 12:11
  • $\begingroup$ I'll provide an answer. $\endgroup$ – ggcg May 13 at 12:13
  • $\begingroup$ Voting to close. Kindly elaborate why you think they should be different or what do you find wrong/confusing about the argument that proves that they would be the same. Welcome to Physics SE! :) $\endgroup$ – Feynmans Out for Grumpy Cat May 13 at 12:30
  • $\begingroup$ Did the editing. $\endgroup$ – Chrys May 13 at 12:34
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If you are referring to the classic projectile problem where the acceleration due to gravity is 9.8m/s/s pointing down (vertically) and you ignore air resistance and other possible factors then, yes the vertical velocity will be the same for both. You can even have one dropped from rest while the other is fired horizontally at 100m/s and they will hit the ground at the same time. Two factors that acconut for this are (1) that gravity causes all masses to accelerate by the same amount, the force of gravity is different but the acceleration is the same, and (2) that the vertical and horizontal motions are completely independent. This will not be true in the presence of aero forces (drag, lift, air resistance, etc).

In theory a feather and a lead ball dropped from the same height will hit the ground at the exact same time. With air resistance you will never see this, but this experiment has been done in a vacuum chamber and video taped. You can probably find videos on Youtube or still pictures in physics books. I hope that helps.

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  • $\begingroup$ Thanks. Got it. $\endgroup$ – Chrys May 13 at 12:25

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