Forces in vectors Calculation 1 Attachment(s) Hi please refer to the image for the question. 
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Do you know what the difference is between $\displaystyle v$, $\displaystyle v_x$ and $\displaystyle v_y$? 
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There is a standard maths technique for separating a vector into separate components, acting in different directions. (2 components for a 2D vector, 3 for a 3D vector, etc.) By convention these components are at 90 degrees with respect to each other. (It is possible to define and use components that are not at 90 degrees, but that is another story). There are standard mathematical rules for what happens to each component of a vector when a mathematical operation is applied to the main vector. If you are familiar with those rules, then the answer is obvious. If you are not familiar with those rules, seek additional guidance from your tutor. The whole point of your tutor giving you these questions is to identify any holes in your understanding, and if they are a good tutor they will then try to fix those holes. 
I don't have tutor. I'm a University student who can't afford a tutor. 
The writers of the problem are trying to mess with you a bit. The answer is B). The xcomponent of the force is $\displaystyle F~cos( \theta )$, so the x component of the force in this case is $\displaystyle c v^2 ~ cos( \theta )$. The trick is that we can break this down into $\displaystyle c v^2~cos( \theta ) = c v \cdot v~cos( \theta ) = c v \cdot v_x$ Frankly I think this is a lousy problem for this level. It's more a test of your Algebra than your Physics knowledge, and the negative sign is somewhat arbitrary. Dan 
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Sound good? :) 
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