Can Kinematics Equations Be Used for an Entire Projectile Trajectory?

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    Kinematics
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Discussion Overview

The discussion centers around the application of kinematics equations to the entire trajectory of a projectile, particularly whether these equations can be used when analyzing motion from launch to landing at the same height. Participants explore the implications of using initial velocity and total flight time in calculations.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant expresses confusion about the applicability of kinematics equations for the entire trajectory of a projectile, specifically questioning if the final velocity can be derived using initial velocity and total flight time.
  • Another participant suggests that plugging in the initial velocity and total flight time should yield the same final velocity, at least in terms of speed.
  • A question is raised regarding which specific kinematics equations are being utilized, with a note that most basic kinematics equations should be applicable for any length of trajectory.
  • A participant proposes testing a specific kinematics equation (V2=U2+2as) in the context of a bullet fired straight up, prompting consideration of the signs for acceleration and displacement after reaching the apex.
  • One participant acknowledges the symmetry of projectile motion and indicates an understanding that careful attention to signs is necessary when applying the equations.

Areas of Agreement / Disagreement

The discussion does not reach a consensus, as participants express varying levels of understanding and confidence regarding the use of kinematics equations for the entire trajectory of a projectile.

Contextual Notes

Participants mention the importance of considering signs in calculations, particularly in relation to the direction of motion and acceleration, but do not resolve specific mathematical steps or assumptions involved in the application of the equations.

Bengo
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I feel like I'm missing a large concept of the kinematics equation. Up until today, I have only used them for HALF of a trajectory (initial velocity and final velocity of 0 at the apex). But can you use them for an ENTIRE trajectory? So say something is fired from the ground and lands on the ground at the same level. If you plug in the initial velocity and use the entire flight time, will you get the same final velocity from these equations?? I'm so confused. Please help me get this sorted out before I take the MCAT.
 
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Bengo said:
If you plug in the initial velocity and use the entire flight time, will you get the same final velocity from these equations??
Sure. Why not give it a shot? (The same speed, at least.)
 
Which kinematics equations are you using?
(most of the basic kinematics equations you get will work fine for a trajectory however long you want though)
 
Try it. What happens if you apply this equation to say a bullet fired straight up?

V2=U2+2as

Remember that if up is +ve then a is -ve.

What happens to s after the apex?
 
genericusrnme, I was just talking about those formulas for a projectile motion from a physics 1 class.

But I see that it works now, the trajectory is symmetric so I guess I just have to be careful about the signs?

Thank you!
 

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