Relative Motion Analysis: Acceleration

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Discussion Overview

The discussion revolves around the analysis of relative motion in a rigid body context, specifically focusing on the use of trigonometric functions (sine and cosine) in vector analysis to determine velocity components. Participants are exploring when to apply these functions versus using given numerical values for velocity in the context of a homework problem.

Discussion Character

  • Homework-related
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions the appropriate circumstances for substituting sine and cosine values in relative motion problems, seeking clarity on their application.
  • Another participant suggests that understanding the underlying concepts is crucial, indicating that sine and cosine are used to resolve vector components against a coordinate system or other vectors.
  • A participant mentions the need for an example to illustrate where confusion arises regarding the use of trigonometric functions.
  • There is a specific inquiry about determining the velocity of slider block C, given the angular velocity and rotation of another block.
  • Further clarification is sought regarding the x and y components of the velocity of block B, with the fixed nature of block A and the restriction of block C to the x-axis noted.
  • One participant suggests calculating the speed and direction of block B to find its velocity components.
  • A later reply provides a specific example of how to apply sine and cosine to find the x-component of velocity, illustrating that these functions are still relevant even when the angle is straightforward.

Areas of Agreement / Disagreement

Participants express varying levels of understanding regarding the use of trigonometric functions in this context. There is no consensus on the best approach, and multiple viewpoints on the application of sine and cosine remain evident.

Contextual Notes

The discussion highlights the need for further examples and clarification of concepts, indicating that some assumptions about participants' prior knowledge may not hold. The specific mathematical steps and definitions involved in the problem are not fully resolved.

Smoker
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Mentor note: moved to homework forum later, therefore no template.[/size]

When doing a rigid body relative motion (accel) problem using vector analysis, how do I know when it's appropriate to substitute sin/cos values vs when to use just the numbers given as the velocity?
 
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It sounds like you are trying to use formulas without understanding them.
vis: sine and cosine are usually used to compute components of vectors resolved against a coordinate system, or against other vectors ... so that is when you use them. You should use whichever trig functions you need to in order to work the problem, not just sine and cosine.

The trouble with this sort of question is that the people who can answer you find this stuff intuitively obvious - this means there is a bit more information needed to get us (me) to understand where the trouble lies.

Please provide an example of where you get in trouble deciding what to use.
 
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Post moved from the technical forums, so no HH Template is shown
I am to determine the velocity of slider block C. Given angular velocity of AB (4.1) and angular rotation of AB (5.5).
Screen Shot 2016-03-03 at 5.01.46 PM.png
 
Okay, and which velocity value where do you want to calculate how, where you ran into the problem of post 1?
 
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mfb said:
Okay, and which velocity value where do you want to calculate how, where you ran into the problem of post 1?
Basically I want to know the x and y components of the velocity of B, A is zero because it's fixed and C is (Vc)i because it's restricted to the x axis, but what is Vb? and why?
 
Okay. Can you find the speed of B, and the direction of motion?
That allows to find the velocity components.

I think this thread fits better to the homework section.
 
Just a note re initial question about when to use sine and cosine:
If the speed of C is ##v_c## then the x-component is ##v_{cx}=v_c\cos\theta## but, here, ##\theta = 180^\circ## (it is the angle ##\vec v_c## makes to the +x-axis). So you get ##\vec v_c = -v_c\hat\imath## ... which is to say, the sine and cosine values are still used, it's just that they are easy.
 

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