What is the best step-by-step method to approach an engineering dynamics problem?

Answer 1

1. Problem
2. Write out the answer with all necessary information that is given to you. It feels like it takes forever, but it’s important to have the problem and solution next to each other.
3. Draw
4. Draw the problem, this is usually a free-body diagram (don’t forget a coordinate frame). Eventually, as you get further into the course, you might need a few drawings. One would be a quick sketch of the problem in the real world, then modelling it into a simplified engineering drawing, and finally the free-body diagram.
5. Known and Unknowns
6. Write out a list of the known/given values with the variable and unit, i.e m = 14 kg (variable = number unit)
7. Write out a list of the unknown values that you will have to solve for in order to solve the problem
8. You can also add any assumptions you made here that change the problem.
9. Also state any constants, i.e. g = 32.2 ft/m² or g = 9.81 m/s²
10. This step helps you to have all of the information in one place when you solve the problem. It’s also important because each number should include units, so you can see if the units match or if you need to convert some numbers so they are all in English or SI. This also gives you the variables side by side to ensure they are unique (so you don’t accidentally have 2 ‘d’ variables and can rename one with a subscript).
11. Approach
12. Write a simple sentence or phrase explaining what method/approach you will be using to solve the problem.
13. For example: ‘use method of joints’, or equilibrium equations for a rigid body, MMOI for a certain shape, etc.
14. This is going to be more important when you get to the later chapters and especially next semester in Dynamics where you can solve the same problem many ways. Might as well practice now!
15. Analysis
16. This is the actual solving step. This is where you show all the work you have done to solve the problem.
17. When you get an answer, restate the variable you are solving for, include the unit, and put a box around the answer.
18. Review
19. Write a simple sentence explaining why (or why not) your answer makes sense. Use logic and common sense for this step.
20. When possible, use a second quick numerical analysis to verify your answer. This is the “gut check” to do a quick calculation to ensure your answer is reasonable.
21. This is the most confusing step as students often don’t know what to put here and up just writing ‘The number looks reasonable’. This step is vitally important to help you learn how to think about your answer. What does that number mean? What is it close to? For example, if you find that x = 4000 m, that’s a very large distance! In the review, I would say, ‘the object is 4 km long which is reasonable for a long bridge’. See how this is compared to something similar? Or you could do a second calculation to verify the number is correct, such as adding up multiple parts of the problem to confirm the total length is accurate i.e. ‘x + y + z = total, yes it works!’

Answer 2

1. Always start by writing out all the given information from the question (ex: mass, external force, angular velocity etc.)
2. Draw the Free Body Diagram (FBD) of the system (multiple FBD's for two or more systems). This is the most important step to solving a dynamics problem.
3. Start with the kinematics portion of the problem using Newton-Euler equations on the system.
4. Now using the rigid-body equations to find the velocity, acceleration, angular velocity and angular acceleration, obtain a system of equations.
5. Solve the system of equations obtained from step 3 and step 4 using method of elimination or substitution to find the required variable.
6. Clearly state the answer with the appropriate units.

Hope this helps!