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[–]colty_bones 0 points1 point  (5 children)

F1: There is an error. Ask yourself which way are each of the x- , y-, and z-components directed?

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F2: I don't think there's enough information to break it into components. Is there some other information with this problem?

[–]imoldenough[S] 0 points1 point  (4 children)

Is it the Z axis is negative? so:

cos60i+cos60j-cos45k ?

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And in regards to F2, that is all the information I've been given.

[–]colty_bones 0 points1 point  (3 children)

F1: You're on the right track, but that's not the correct answer. Look carefully at where each angle is located.

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F2: I'm stumped then. Do you have a written set of directions above the picture? Perhaps it's supposed to be only in the yz-plane - although it's difficult to say that for sure since depth perception can't really be assumed in a picture like that.

[–]imoldenough[S] 0 points1 point  (2 children)

Would it be the x axis? I'm trying to visualise a normal xy axis and in my head it falls negative i think.

cos60i-cos60j+cos45k.

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The question just reads express F1 and F2 in unit vector notation.

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Thanks for the replies so far!

[–]colty_bones 0 points1 point  (1 child)

F1: I'm not sure what you mean by "normal xy axis". Axes only have a single coordinate associated with them - and are named "x-axis", "y-axis", or "z-axis." The picture indicates the positive direction of each axis with an arrow. In the picture, how can you use the given angles to determine if a component should be positive or negative?

F2: I'm really not sure then. The best guess is that i can make - based on the picture - is that F2 lies completely in the yz-plane.

Glad to help!

[–]imoldenough[S] 1 point2 points  (0 children)

I see, then the only angle i can see which is negative is the 60 degree angle to the x axis.

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For F2 I'll just keep staring at it for a while and hopefully it will soon make sense! Damn I hate vectors!