Projectile Motion: Initial Velocity Derivation

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Homework Help Overview

The discussion revolves around the derivation of an accurate mathematical model for projectile motion, specifically in the context of water rockets launched at various angles. The original poster is comparing theoretical results with experimental data and is questioning the validity of their model, particularly regarding the initial velocity calculation.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • The original poster attempts to derive a model for projectile motion without accounting for drag and is seeking feedback on the accuracy of their initial velocity estimation. Some participants question the validity of a specific equation used in the model, particularly its implications when launching at a horizontal angle.

Discussion Status

The discussion is ongoing, with participants providing feedback on the original poster's model and raising questions about specific equations. There is an acknowledgment of assumptions made in the model, particularly regarding the launch conditions.

Contextual Notes

There is a mention of the model's limitations, such as the assumption of launching from ground-level and the neglect of drag forces. The original poster expresses uncertainty about the accuracy of their initial speed calculation.

PhysicsIBStudent
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Hey guys, I am working on a school project and have fired some water rockets at different angles. I am now trying to compare theoretical results vs experimental results. But I am struggling to produce an accurate mathematical model.

I have attached my attempt to this post. It is quite long and possibly overly complex. I have not taken drag into account for this model.

I have compared the range results I got from my model to some from a water rocket simulator which was fed the same initial conditions but they are very different.

My question is whether my model is anywhere close to correct or where I went wrong. I used data from my water rocket to attempt to find the initial velocity of the rocket. I don't think my initial speed is correct tho.
 

Attachments

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Can you upload a PDF version of the file please? DOCX file format is not as secure as PDF format. Thanks.
 
berkeman said:
Can you upload a PDF version of the file please? DOCX file format is not as secure as PDF format. Thanks.

Done. Please let me know if there are issues opening the pdf
 
Equation (12) is suspicious. According to (12) what is the range when the projectile is launched horizontally (θ = 0)?
 
Tom.G said:
Equation (12) is suspicious. According to (12) what is the range when the projectile is launched horizontally (θ = 0)?

Your right I forgot to mention this equation assumes you are launching from ground-level and the ground is flat. The formula only intends to work for non zero angles as launching at 0 degrees would result in a crash of some sort.
 

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