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 KyleFresh Dec 8th 2018 02:10 PM

Forces in vectors Calculation

1 Attachment(s)
Hi please refer to the image for the question.

 benit13 Dec 10th 2018 06:23 AM

Quote:
 Originally Posted by KyleFresh (Post 42317) Hi please refer to the image for the question.
So... what do you think?

Do you know what the difference is between $\displaystyle v$, $\displaystyle v_x$ and $\displaystyle v_y$?

 KyleFresh Dec 11th 2018 12:54 PM

Quote:
 Originally Posted by benit13 (Post 42320) So... what do you think? Do you know what the difference is between $\displaystyle v$, $\displaystyle v_x$ and $\displaystyle v_y$?
I got Fnetx= vcosθ - cv^2cosθ

 benit13 Dec 12th 2018 02:00 AM

Quote:
 Originally Posted by KyleFresh (Post 42324) I got Fnetx= vcosθ - cv^2cosθ
Okay... but do you know what the difference is between $\displaystyle v$, $\displaystyle v_x$ and $\displaystyle v_y$? It's important because once you know that, you'll find the question a lot easier.

 Woody Dec 12th 2018 02:53 AM

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.

 KyleFresh Dec 13th 2018 08:32 PM

I don't have tutor. I'm a University student who can't afford a tutor.

 topsquark Dec 14th 2018 06:33 AM

The writers of the problem are trying to mess with you a bit. The answer is B).

The x-component 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

 Pmb Dec 16th 2018 12:51 PM

Quote:
 Originally Posted by KyleFresh (Post 42332) I don't have tutor. I'm a University student who can't afford a tutor.
I can tutor you for free if you'd like. I did a lot of tutoring in college and have spent years in forums helping people. What I won't do is simply give answers or help when you haven't shown your attempt.

Sound good? :)

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