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Physics - Vectors

Hello TSR,

I recently started AS Physics and I'd really like a good grade. I didn't get the best grade at GCSE, so I'm going to start working hard from the get-go.

So, I've been having a bit of trouble with vectors.

In this example:
5dc0f91d5f7507da11bf308bf723c08f.png

The teacher formed a tip-to-tail vector triangle in order to find the magnitude of the resultant vector and the direction. I understand how he found the magnitude, but for some reason he drew a vertical above the initial point (which I'm assuming is the y-axis) and measured the angle from the vertical to the resultant. I was taught that you measure the angle inside the triangle from the initial vector to the resultant vector. Has he did this incorrectly?
(edited 7 years ago)
What does the question s/he's answering ask for? An angle has got to be referenced to something e.g. '5 degrees above horizontal', 30 degrees from vertical or '45 degrees from the direction you were facing 10 minutes ago'
You need to measure the angle between the vector you worked out and the thing the question asked you to reference it to... You'd measure from vertical if you were asked to find the angle between a ladder and a wall but you'd measure from horizontal if you were asked to find the angle between a ladder and the floor.

Ps it looks like it might be a bearing, the convention for bearings is that you measure the angle clockwise from north... And north is usually up on diagrams.
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Original post by Joinedup
What does the question s/he's answering ask for? An angle has got to be referenced to something e.g. '5 degrees above horizontal', 30 degrees from vertical or '45 degrees from the direction you were facing 10 minutes ago'
You need to measure the angle between the vector you worked out and the thing the question asked you to reference it to... You'd measure from vertical if you were asked to find the angle between a ladder and a wall but you'd measure from horizontal if you were asked to find the angle between a ladder and the floor.

Ps it looks like it might be a bearing, the convention for bearings is that you measure the angle clockwise from north... And north is usually up on diagrams.


I'm the OP. For some reason I can't sign on to my other account.

I understand what you're saying now. However, what if the question doesn't state if it has to be in reference to something or a bearing? For example, I've been doing this in M1 as well and when they ask for displacements, they use bearings but don't state that they want the direction as a bearing.
Original post by 0To100000
I'm the OP. For some reason I can't sign on to my other account.

I understand what you're saying now. However, what if the question doesn't state if it has to be in reference to something or a bearing? For example, I've been doing this in M1 as well and when they ask for displacements, they use bearings but don't state that they want the direction as a bearing.


The general rule is to follow how the question has presented the values, so if they give bearings, then you're expected to give a bearing and if the values you are given are to 2 s.f., then your answer will also be to 2 s.f.
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Original post by TheOtherSide.
The general rule is to follow how the question has presented the values, so if they give bearings, then you're expected to give a bearing and if the values you are given are to 2 s.f., then your answer will also be to 2 s.f.

How would you know what convention to use for this then??
5cb696fd0274f4da68c8cf81dc8202a3.png
Original post by 0To100000
How would you know what convention to use for this then??
5cb696fd0274f4da68c8cf81dc8202a3.png


If they talk about compass directions, then bearings would make the most sense here. And I suppose giving the distance to more significant figures doesn't hurt, and actually, I guess you could give your answer to more significant figures to be safe.
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Original post by TheOtherSide.
If they talk about compass directions, then bearings would make the most sense here. And I suppose giving the distance to more significant figures doesn't hurt, and actually, I guess you could give your answer to more significant figures to be safe.


Thanks you just saved me a lot of heartache and frustration

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