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MEI M1 Help...?

hey I need some help on mei m1 for the exam in 11days, but not a specific question but rather a type of question and it will be something like this...

Calculate the angle the vector 3i+6j 3i+6j (Can be any vector mines just an example) makes with the positive i direction. (again It will ask for other things like the angle with the vertical or negative horizontal or as a bearing)


I literally always get this wrong as I never know what angle they are talking about and hence don't know what to do to find the angle.

Any help is greatly appreciated!!!!!
Reply 1
Avatar for Dj.Clay
Dj.Clay
4
Well show us how you'd try and solve the example you gave us, so we know how much of the method you know, and how much you understand ^^
Reply 2
Avatar for Coolcat
Coolcat
OP
Original post by Dj.Clay
Well show us how you'd try and solve the example you gave us, so we know how much of the method you know, and how much you understand ^^


that was just something I made up but I literally don't understand the angle that is asking for that is all I understand perfectly how to work it out If i understand what they are talking about my problem is that i never no which angle they want!!!!!! :colondollar:
Reply 3
Avatar for the bear
the bear
20
Typically the i direction is east and the j is north...
so draw 3 east followed by 6 north...
Reply 4
Avatar for Dj.Clay
Dj.Clay
4
Does this help? It's just like basic graphwork, plot i against j and mark on the point, and you can see the angle it makes with the positive i-axis :smile:
Scan0029.jpg169.5KB
Reply 5
Avatar for Coolcat
Coolcat
OP
Original post by Dj.Clay
Does this help? It's just like basic graphwork, plot i against j and mark on the point, and you can see the angle it makes with the positive i-axis :smile:


thats fine but I understand that anyway the other ones im not sure are like
"as a bearing" and "negative/pos i direction" etc etc was just wondering if there is an easy way to learn???

and i am especially stuck on bearings if you could help me!!!!

cheers
Reply 6
Avatar for Dj.Clay
Dj.Clay
4
Basically they give you a vector, plot it on the graph of j against i, and drawn a line between the points and the origin.

If they say positive i-direction, then consider the i-axis from the origin going off to the right (towards positive infinity)

The angle is the angle between those 2 lines.

We generally consider anti-clockwise to be positive angles.

As for bearings, a bearing is the angle from 000 degrees to 360 degrees (always written with 3 numbers even if they are zero), and it is the angle clockwise from due north (or upwards, or for vectors the positive j-direction)

If you still aren't sure, ask away, if not see if you can give me the angle from the positive i-axis of -3i+3j
Reply 7
Avatar for Coolcat
Coolcat
OP
Original post by Dj.Clay
Basically they give you a vector, plot it on the graph of j against i, and drawn a line between the points and the origin.

If they say positive i-direction, then consider the i-axis from the origin going off to the right (towards positive infinity)

The angle is the angle between those 2 lines.

We generally consider anti-clockwise to be positive angles.

As for bearings, a bearing is the angle from 000 degrees to 360 degrees (always written with 3 numbers even if they are zero), and it is the angle clockwise from due north (or upwards, or for vectors the positive j-direction)

If you still aren't sure, ask away, if not see if you can give me the angle from the positive i-axis of -3i+3j


would it be inverse tan (3/3) so..... 45 degress or pi/4 but ill stick to degrees to make life easier on myself!
Reply 8
Avatar for Coolcat
Coolcat
OP
Original post by Dj.Clay
Basically they give you a vector, plot it on the graph of j against i, and drawn a line between the points and the origin.

If they say positive i-direction, then consider the i-axis from the origin going off to the right (towards positive infinity)

The angle is the angle between those 2 lines.

We generally consider anti-clockwise to be positive angles.

As for bearings, a bearing is the angle from 000 degrees to 360 degrees (always written with 3 numbers even if they are zero), and it is the angle clockwise from due north (or upwards, or for vectors the positive j-direction)

If you still aren't sure, ask away, if not see if you can give me the angle from the positive i-axis of -3i+3j


or would it be 90 degrees + the 45 degrees so it is positive i direction ... so 135 degrees????
Reply 9
Avatar for Dj.Clay
Dj.Clay
4
Yes, 135 degrees :smile: Just need to combine your knowledge of trig with actually looking at where the point is and use some common sense to figure out the angle :wink:

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