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Vectors in mechanics 1 watch

1. Theres a question that say:
Find the magnitude and direction of the resultant of the sum of the three forces represented by 2i-5j, 3j and i+2j

Any help? i have no idea how to start it. Thanks
2. Vector addition. i-components added together and j-components added together equal the i and j components of the resultant.
3. (Original post by D-Day)
Vector addition. i-components added together and j-components added together equal the i and j components of the resultant.
Hi again! lol well ive added them together and got 3i as a result but then wat do u write for the magnitude and direction? i suppose 3i can be magnitude but what about direction?
4. That says the resultant has 3 units in the x and zero in the y. What angle is formed by only positive x values (no y)?
5. (Original post by D-Day)
That says the resultant has 3 units in the x and zero in the y. What angle is formed by only positive x values (no y)?
ok then its 90 degrees so how would i write it formally if you knwo what i mean lol i just keep thinking 3i at 90 degrees just sounds a bit odd
6. Add them together, draw a right angled triangle (i is across, j is vertical), find the hypotenuse. That's the magnitude. Then do tan = o/a to find angle.

EDIT: Oh, the j component is 0. Just ignore me now lol.
7. you'll have to find the angle between the two components which will give directioon

i have not read your question properly, but in general vectors's direction is as an angle when doing Mechanics calculations
8. 90? Not quite.

------------------>
(3 unit vector)

What angle does that form with the positive x-axis?
9. (Original post by JBKProductions)
ok then its 90 degrees so how would i write it formally if you knwo what i mean lol i just keep thinking 3i at 90 degrees just sounds a bit odd
90 degrees from positive x axis.
10. (Original post by DaveJ)
90 degrees from positive x axis.
ok thanks!
11. (Original post by D-Day)
90? Not quite.

------------------>
(3 unit vector)

What angle does that form with the positive x-axis?

It is 90 surely.

I mean, the x axis is horizontal, there's a line going up from it. So to reach the vertical line from the horizontal line, you go through 90 degrees - the two lines are perpendicular.
12. The line is horizontal. Do the addition

edit: 2i+i=3i, -5j+3j+2j=0j. 3i+0j=3i. Horizontal line of length 3.
13. (Original post by D-Day)
The line is horizontal. Do the addition

edit: 2i+i=3i, -5j+3j+2j=0j. 3i+0j=3i. Horizontal line of length 3.
Hmm...... I appear to have been treating the x axis as vertical.

14. (Original post by JBKProductions)
ok thanks!

Apologies, I was incorrect.

Zero degrees from positive x axis.

That really should be right now. If I'm wrong, I shall go away and cry.
15. (Original post by D-Day)
The line is horizontal. Do the addition

edit: 2i+i=3i, -5j+3j+2j=0j. 3i+0j=3i. Horizontal line of length 3.
oh starting from the x-axis i get it now lol 0 degrees
16. Ok cool. Y'all had me questioning something I stopped having to think about years ago
17. (Original post by D-Day)
Ok cool. Y'all had me questioning something I stopped having to think about years ago
UK forum; UK parlance

"You 'orrible lot"
18. (Original post by D-Day)
Ok cool. Y'all had me questioning something I stopped having to think about years ago
just a question though why does it start from the x-axis and not y? i always thought you start measuring your angles from the y axis but guess i was wrong
19. (Original post by JBKProductions)
just a question though why does it start from the x-axis and not y? i always thought you start measuring your angles from the y axis but guess i was wrong
You can measure angles from wherever you like, as long as you specify what you're doing. The answer would be "0 degrees from the positive x axis" or "90 degrees from the positive y axis" etc. Both are perfectly valid, but we tend to take the normal to be +x. Still, make sure you specify it in exams.
20. (Original post by JBKProductions)
just a question though why does it start from the x-axis and not y? i always thought you start measuring your angles from the y axis but guess i was wrong
I forget the rule as for why positive x is "zero" but I know this is the case.

edit: ashy, you smart *******

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