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# M1 Bearing

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1. Hi
im doing http://www.mei.org.uk/files/papers/2011_june_m1.pdf
anyway im stuck on question 6 ii. The direction of motion is 4i+5j
Ive made a right angle triangle with one side 4 (in the x direction) and one side 5 (in the y direction)

i cant figure out which angle i should be working out (arctan5/4 or arctan4/5) and why. i dont know how to get the bearing from this too
any help

thanks
2. (Original post by starwarsjedi123)
Hi
im doing http://www.mei.org.uk/files/papers/2011_june_m1.pdf
anyway im stuck on question 6 ii. The direction of motion is 4i+5j
Acceleration is -2j.

So velocity at t=2.5 is 4i-5j

Ive made a right angle triangle with one side 4 (in the x direction) and one side 5 (in the y direction)

i cant figure out which angle i should be working out (arctan5/4 or arctan4/5) and why. i dont know how to get the bearing from this too
any help

thanks
See attached.

A bearing is a clockewise angle from due North - the angle in green.

You can work out either angle a, or angle b.

Bearing is 90+a, or 180-b

where a is arctan5/4 and b is arctan4/5

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