Solve Problem w/ Vectors Forces of Magnitude 3,5,7 N | x Component 4.968

[MMCS]

Question

Forces of magnitude 3 Newtons, 5 Newtons and 7 Newtons act along the vectors (-3,-2,-9) (8,5,-9) (4,-1,-9)

Find the x component.

I have the answer at 4.968 however i can not arrive at it, attached is my working out. d has been used instead of c.i have the x components as 2.531, -2.774 and -6.93 however these are not correct as they do not equal the answer of 4.968

**Im pretty sure the figures are correct, there is most probably error in the method

Thanks

 

[Joffan]

Normalize the given vectors to unit length.

 

[MMCS]

Is that not what i have done.For example, on F1 i have divided it by the magnitude of AB (13.038) then multiplied it by the magnitude of Newtons given in the question (3N) ?

 

[Joffan]

I don't know why you chose to multiply the vectors together first - there was no need.

 

[MMCS]

I didnt multiply them, it isn't clear from the working out sorry, where it says ab it represents the vector a to b.

 

[Joffan]

Ah. The three triplets are the vectors - the forces act from the origin towards those coordinates.

 

[NemoReally]

Does the following help?

Notes:

• str2mat is user-defined function that converts a string representation of a vector into a Mathcad array

• the over-arrow is the vectorize operator (you probably know this, but ...)

 

[MMCS]

Im only new to mathcad so i wasnt aware of them functions but ill give them a go they look to solve the problem pretty easily thanks!

 

[Joffan]

I recommend solving this without Mathcad, to get a feel for the process. Your initial problem with solution was not associated with Mathcad use, but with understanding what was specified in the problem.

 

[berkeman]

Does the following help?

Notes:

• str2mat is user-defined function that converts a string representation of a vector into a Mathcad array

• the over-arrow is the vectorize operator (you probably know this, but ...)

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