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AQA M1 help needed - finding a vector given bearing and distance

What the title says. Trying to self teach M1 and with 2 weeks to go, its going to be something of a crash course. Currently stuck, and the Heinemenn book doesn't do a great job of explaining how to find a vector given distance and bearing. Any help would be appreciated.
Reply 1
Avatar for Hjyu1
Hjyu1
2
Do you have an example ?
Reply 2
Avatar for metrize
metrize
18
You can do trig.
You can figure out the angle, and then d sin theta and d cos theta to find the other sides

@_Tyrion
(edited 7 years ago)
Reply 3
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_Tyrion
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Original post by metrize
You can do trig.
You can figure out the angle, and then d sin theta and d cos theta to find the other sides

@_Tyrion


Yeah, this is what I do, but my problem is drawing the triangle. I'm OK with drawing the first line (the bearing and the distance one) but then theres loads of options for drawing a right angled triangle. I end up just guessing, and I'm correct about 50% of the time.

If you don't know what I mean, I can take a picture? Anyone?
Reply 4
Avatar for metrize
metrize
18
Original post by _Tyrion
Yeah, this is what I do, but my problem is drawing the triangle. I'm OK with drawing the first line (the bearing and the distance one) but then theres loads of options for drawing a right angled triangle. I end up just guessing, and I'm correct about 50% of the time.

If you don't know what I mean, I can take a picture? Anyone?


Send me the question
Reply 5
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_Tyrion
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Original post by metrize
Send me the question


A ball is thrown so that its initial velocity is 8ms^-1 at an angle of 50 degrees above the horizontal. The united vectors i and j are horizontal and vertical, respectively. Express the initial velocity of the ball in terms of the unit vectors i and j.

What I did is start off drawing an x and y axis, then drew a line at 50 degrees with length 8. How do I finish off the triangle after this? I can either draw a horizontal line that touches the y axis to complete the triangle or a vertical line that touches the x axis to complete the triangle.

My final answer was 6.13i + 5 14j.
Reply 6
Avatar for metrize
metrize
18
Original post by _Tyrion
A ball is thrown so that its initial velocity is 8ms^-1 at an angle of 50 degrees above the horizontal. The united vectors i and j are horizontal and vertical, respectively. Express the initial velocity of the ball in terms of the unit vectors i and j.

What I did is start off drawing an x and y axis, then drew a line at 50 degrees with length 8. How do I finish off the triangle after this? I can either draw a horizontal line that touches the y axis to complete the triangle or a vertical line that touches the x axis to complete the triangle.

My final answer was 6.13i + 5 14j.


I and J always form a right angle
I got j=6.13 and i=5.14

See below
(edited 7 years ago)
20160610_174811.jpg507.9KB
Reply 7
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_Tyrion
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Original post by metrize
I and J always form a right angle
I got j=6.13 and i=5.14

See below


Why is the angle 50 degrees? Howcome it isn't 40 degrees? Because the angle between the line which is 5ms^-1 and the y axis is 50 degrees, so the angle in the triangle is 90-50=40?
Reply 8
Avatar for metrize
metrize
18
Original post by _Tyrion
Why is the angle 50 degrees? Howcome it isn't 40 degrees? Because the angle between the line which is 5ms^-1 and the y axis is 50 degrees, so the angle in the triangle is 90-50=40?


Its 50 from the horizontal, so since i is horizontal its 50 from i
Reply 9
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_Tyrion
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Original post by metrize
Its 50 from the horizontal, so since i is horizontal its 50 from i


Aah right, thanks. If they hadn't specified that it is 50 degrees from the horizontal and instead just said it was on a bearing of 050 degrees, would it have been how I said it or not?
Original post by _Tyrion
Aah right, thanks. If they hadn't specified that it is 50 degrees from the horizontal and instead just said it was on a bearing of 050 degrees, would it have been how I said it or not?

Yep, then you would have been right

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