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September 22, 2019, 09:28:46 am

### AuthorTopic: VCE Specialist 3/4 Question Thread!  (Read 1096575 times) Tweet Share

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#### undefined

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##### Re: VCE Specialist 3/4 Question Thread!
« Reply #9525 on: August 17, 2019, 03:14:37 pm »
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Hello everyone, I feel like I'm missing something completely obvious, but I cannot understand why c=0 here.This is VCAA 2007 Exam 1 Q6a. Would really appreciate it if someone could explain.

so r(t)=2cos(2t)i+3sin(2t)j+c, where c is a vector

r(0)=2cos(0)i+3sin(0)j+c=2i
so 2i+c=2i
so c=0
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#### AnonymooseUser

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##### Re: VCE Specialist 3/4 Question Thread!
« Reply #9526 on: August 17, 2019, 09:10:36 pm »
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r(0)=2cos(0)i+3sin(0)j+c=2i
so 2i+c=2i
so c=0

$\mathbf{v}(t)=-4\sin(2t)\mathbf{i}+6\cos(2t)\mathbf{j},\quad 0\le t\le \pi/2.$

$2\mathbf{i}=2\cos(0)\mathbf{i}+3\sin(0)\mathbf{j}+\mathbf{c}\implies 2\mathbf{i}=2\mathbf{i}+0\mathbf{j}+\mathbf{c}\implies \mathbf{c=0}$.

I just realised that I was registering cos (0) as pi/2 instead of 1... Thank you both and sorry for the dumb question.

#### Bzalmay

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##### Re: VCE Specialist 3/4 Question Thread!
« Reply #9527 on: August 23, 2019, 08:10:54 pm »
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Do you guys Recommend Doing Specialist 3/4 without 1/2?

#### AlphaZero

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##### Re: VCE Specialist 3/4 Question Thread!
« Reply #9528 on: August 23, 2019, 08:51:04 pm »
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Do you guys Recommend Doing Specialist 3/4 without 1/2?

In general, no, I wouldn't recommend someone to do units 3&4 without units 1&2, but of course, there are a few handful of capable students out there that I actually would recommend they pushed themselves for it. It really depends on the ability of the student and their motivations for considering the subject.
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#### Otter

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##### Re: VCE Specialist 3/4 Question Thread!
« Reply #9529 on: September 06, 2019, 07:40:07 pm »
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When should we write a tilda ~ sign under acceleration (for example, F=ma)?
Do we even need the tilda sign at all?
How about for vector calculus and kinematics?

#### JOS0019

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##### Re: VCE Specialist 3/4 Question Thread!
« Reply #9530 on: September 06, 2019, 07:49:18 pm »
+1
When should we write a tilda ~ sign under acceleration (for example, F=ma)?
Do we even need the tilda sign at all?
How about for vector calculus and kinematics?

In F = ma, Force and Acceleration are vectors so they must have the tilde
However, the study design does not specify that they should, so you shouldn't worry about it.
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#### AlphaZero

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##### Re: VCE Specialist 3/4 Question Thread!
« Reply #9531 on: September 06, 2019, 07:55:35 pm »
+1
When should we write a tilda ~ sign under acceleration (for example, F=ma)?
Do we even need the tilda sign at all?
How about for vector calculus and kinematics?

You should write tildes when the particle is moving in 2D or 3D space (ie. when looking at vector functions). Clearly, if you write a tilde for acceleration, you must write one for force too.

We tend to omit it for rectilinear motion since there isn't really a useful notion of 'direction'. The positive and negative directions are determined by the signs of the quantities.
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#### Otter

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##### Re: VCE Specialist 3/4 Question Thread!
« Reply #9532 on: September 13, 2019, 08:00:01 pm »
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When labelling a force diagram, for which components do we need to have tildes?
eg. tension, force, weight, reaction, friction (all of them?)

(apologies if I sound pedantic - I'm trying my best to avoid losing marks for silly mistakes!)

#### Tau

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##### Re: VCE Specialist 3/4 Question Thread!
« Reply #9533 on: September 13, 2019, 09:03:31 pm »
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When labelling a force diagram, for which components do we need to have tildes?
eg. tension, force, weight, reaction, friction (all of them?)

(apologies if I sound pedantic - I'm trying my best to avoid losing marks for silly mistakes!)

I don’t think you actually need to label them with tildes. You’re actually just specifying  the name for the magnitude, the direction is indicated by the arrow. You can see this in, for example, 2018 Exam 1.
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