Calculating Projectile Distance with MATLAB: Physics Homework Help

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Discussion Overview

The discussion revolves around a homework problem requiring the calculation of the horizontal distance a projectile travels when launched from a spring-loaded cannon at a 45-degree angle. Participants explore how to set up a MATLAB script to determine the necessary spring compression for the projectile to land at specified distances (10, 12, and 14 feet). The conversation includes aspects of physics, programming, and problem-solving strategies.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses uncertainty about how to begin the MATLAB coding process for the projectile distance calculation.
  • Another suggests converting to SI units to avoid confusion, although this is not seen as the main issue by the original poster.
  • Some participants emphasize the importance of understanding the problem conceptually before coding, suggesting that the original poster should solve it by hand first.
  • There are questions regarding the original poster's experience with MATLAB and programming, with some participants expressing concern about the assignment's requirements given their limited experience.
  • Suggestions are made to utilize online resources for learning MATLAB, including tutorials and forums, while emphasizing that direct coding assistance is not provided in the forum.
  • Discussion includes the idea of using iterative methods or numerical solutions in MATLAB, such as Newton's method, to find the required spring compression.
  • Some participants argue that engineering students should develop coding skills for problem-solving, regardless of the specific programming language used.

Areas of Agreement / Disagreement

Participants do not reach a consensus on how to approach the problem, with differing opinions on the necessity of understanding the physics versus the programming aspect. There is also disagreement on the adequacy of the original poster's experience with MATLAB for the task at hand.

Contextual Notes

Participants note that the problem may not have a straightforward solution and could require iterative calculations or numerical methods, which adds complexity to the coding task. The original poster's understanding of the physics involved and the specific requirements of the assignment remain unclear.

cphill29
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Homework Statement


I have to write a MATLAB script that calculates the horizontal distance of a projectile fired from a cannon set at 45 degrees by a compressed spring. I know that the spring constant is 6 lb/in, the unstretched length of the spring is 1 foot, the mass of the projectile is 0.1 lb, and the projectile has to land 10, 12, and 14 feet away. How much spring compression is needed to hit these three lengths?

Homework Equations


KE+PE=KE+PE

The Attempt at a Solution


I really have no idea how to even begin. I have this so far

>>g=-32.2
>>m=0.1
>>k=6
>>d=1

I think I need some kind of loop? I really need some help here.
 
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I would start by adding some units, maybe converting to SI units. Sure it can be done using imperial but if you are not sure where to start, I think imperial units mat confuse you more. You have the Mass of the projectile in pounds (mass) and spring constant using pounds(force) to start.
 
That's not the issue. I need help setting up the MATLAB code. I can deal with the units later.
 
cphill29 said:
That's not the issue. I need help setting up the MATLAB code. I can deal with the units later.
Have you worked with programming langues before?
Typically you KNOW what you want the program to solve first. The implimentation comes later.

Do you know how to solve problems like this, and your question is purely about how MATLAB works?
Or are you struggling with how to solve the problem?
Or do you not know how to solve problems with programming langues?
 
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start by determining how you would solve this by hand. Once you know that, you simply move the implementation into the code.
 
donpacino said:
Have you worked with programming langues before?
Typically you KNOW what you want the program to solve first. The implimentation comes later.

Do you know how to solve problems like this, and your question is purely about how MATLAB works?
Or are you struggling with how to solve the problem?
Or do you not know how to solve problems with programming langues?

I have next to no experience with matlab. I would try and solve for the initial velocity that I need for each given distance, but I'm not sure how to make that into a MATLAB code. Getting that by trial and error by hand would take an eternity.
 
cphill29 said:
I have next to no experience with matlab. I would try and solve for the initial velocity that I need for each given distance, but I'm not sure how to make that into a MATLAB code. Getting that by trial and error by hand would take an eternity.
Why do you have an assignment to use MATLAB to do this, and you have NO experience or instruction in using MATLAB? Something is not adding up here...
 
berkeman said:
Why do you have an assignment to use MATLAB to do this, and you have NO experience or instruction in using MATLAB? Something is not adding up here...
Because MATLAB isn't required for chemical engineering majors at my school, but dynamics is, and this is a dynamics problem. I also didn't say I have no experience at all, but next to none, meaning very little. I can do basic computations but this one is out of my league.
 
Then I'd recommend spending some time with some MATLAB learning resources. There are many of them, from the MATLAB website to YouTube videos to other tutorial and example web pages. We cannot write your code for you here -- that's not how the PF schoolwork help forums work.
 
  • #10
Is your problem statement the exact wording of the assignment? From what I read is not clear just *how* you are to make use of MATLAB to solve the problem.

MATLAB is capable of simply doing the math for expression that you type in, but it can also numerically "integrate" differential equations, or home in on solutions by iteration, or...

There are a lot of different ways to employ such a versatile tool. For example, you could use vector/matrix variables to solve several instances ("inputs") for the problem at once, or simply chug through the math separately for each of the inputs. Write a function to return the desired result for a given input perhaps.
 
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  • #11
You could write the formula that you want to solve. Then if it is something where there is not a nice closed form solution to get the amount of spring compression then you can use Matlab or something else (even a spreadsheet) to go through the iterations or do something like Newton's method.
 
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  • #12
It's my opinion that every engineering major should be able to write some kind of code to do some loops and some basic iterative calculations (like Newton's method, Euler's method, etc). Whether it's Matlab or something else like Excel or Python, it's good to know how to whip something like that up. It's part of being a problem solver. It is good practice for you. As to how you figure how to code it in Matlab, there are lots of online resources for that as somebody else said.

stackoverflow.com or youtube are places to start.
 
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  • #13
cphill29 said:
I have next to no experience with matlab. I would try and solve for the initial velocity that I need for each given distance, but I'm not sure how to make that into a MATLAB code. Getting that by trial and error by hand would take an eternity.

People have been solving these problems by hand way before computers. Computers simply preform the computations to make life easier.
How would you solve this problem if you were given it on a test. This is easily a problem that could be given in a physics test, maybe even a no calculator physics test. (note: by include on a test I mean setup the equations)
 
  • #14
to start, why don't you setup the equations for determining how fast the projectile has to be the moment it leaves the spring
 
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