Questions on Solution in Mechanics

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The discussion focuses on understanding why a certain value is equated to zero in a mechanics problem. It emphasizes the method of finding the minimum value of a function through differentiation and setting the derivative to zero, which helps identify both maximum and minimum values. A diagram is referenced to illustrate how moving point P affects the distance to point Q when the vectors are no longer perpendicular. Additionally, the components of the vector pVQ are mentioned as relevant to the analysis. Overall, the conversation centers on applying calculus principles to solve mechanics-related questions.
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EDIT: On the first image, I meant why is it equated to Zero, not X​


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1. Do you know how to find the minimum value of a function? You differentiate it and set the derivative to 0. This will give you both maximum and minimum values, but if you already know the function can't have a maximum, you can assume that you've found a minimum.

2. See the diagram at the right. You can see that if P is moved a little, so that the two vectors are no longer perpendicular, the distance from P to Q would get longer.

3. They come from the components of the vector pVQ.
 

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