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March 28, 2024, 10:11:26 pm

Author Topic: VCE Physics Question Thread!  (Read 603186 times)  Share 

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Rishi97

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Re: VCE Physics Question Thread!
« Reply #630 on: October 07, 2014, 05:28:57 pm »
+1
Why is it that no work is done when the component is in a perpendicular direction to the objects movement?

thanks in advance :)

I'm not too sure of the "real" reason but I'm a more mathematical person so I think of it using the formula
W=Fxcos(angle)
If the angle is 90 which as you said is perpendicular, the work will equal 0
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myanacondadont

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Re: VCE Physics Question Thread!
« Reply #631 on: October 07, 2014, 06:01:20 pm »
0
Heyyy; Just curious as to where NEAP are in terms of difficulty of papers. We had the 2014 trial exam at school. I got ~85% however it's a bit disheartening after doing VCAA ones and getting high-mid 90's. Should I be worried or are they just tough?

silverpixeli

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Re: VCE Physics Question Thread!
« Reply #632 on: October 07, 2014, 06:49:26 pm »
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Can someone please clarify this concept?
The forward driving force is provided by the friction exerted by the ground on the rear wheel. It is the action – reaction pair to the friction force of the wheel pushing backwards on the ground
Retarding forces acting on the bicycle include air resistance (drag) and friction on the wheels (especially when the brakes are applied).
So what does friction do? How is part of the driving force and the retarding force? So if the bicycle is travelling where there is no air resistance, it won’t ever stop? Because the retarding force is trying to stop it, but instead it actually helps it to move, but as it moves the friction on the wheels try to stop it, and then the cycle repeats itself?
As I understand it depends on what the wheels are trying to do;

If you're pedalling and trying to turn the wheels, consider the contact point of each wheel with the ground. It's trying to push the ground back because that's the way the wheel is turning when you try to pedal, and the reaction force pushes the entire bike/rider system forward. In addition to this there's a little bit of 'rolling resistance' which is a force opposing the propulsion due to the surface but for most surfaces and certainly most VCE physics questions this can be ignored.

If you're braking it's a slightly different story. Brakes apply a torque to the wheels to stop them from rotating rather than a torque to make them rotate which is the case above. As the wheels are slowing down, the situation is reversed. The wheel pushes against the ground the other way at the point of contact with the surface, and the surface pushes back and you slow down.

At all times, there's going to be air drag which is proportional to your velocity.

Hope that helps!
« Last Edit: October 07, 2014, 06:51:19 pm by silverpixeli »
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Re: VCE Physics Question Thread!
« Reply #633 on: October 07, 2014, 09:26:18 pm »
+3
Why is it that no work is done when the component is in a perpendicular direction to the objects movement?

thanks in advance :)
Work is what I like to call - "useful energy". The consumed energy that actually contributed towards an object's propagation in a certain direction.
Lets say that there are a billion forces acting on an object which all add up to a net force accelerating in a northerly direction. Now lets pick one of these forces which happens to be acting in a NW direction. We can say that this force has done some work because it has a north bound force component which has contributed some energy to the object's propagation in the northerly direction.

However, I would call a westerly-bound force a lazy, if not counter productive, force. All it is doing is expending all its energy trying to drag the object to the west instead of to the desired north. Simply because it doesn't have a north bound force component to contribute some work in the northerly direction.
 
Hence, no work is done by a force acting in a direction perpendicular to the object's movement.
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Re: VCE Physics Question Thread!
« Reply #634 on: October 07, 2014, 11:07:21 pm »
0
Hey everyone
I have a some questions about a dodgy momentum prac report.

The aim of this experiment was to investigate whether momentum is conserved in elastic and/or inelastic two dimensional collisions.
An air table provides a surface with minimal friction for the pucks to move across.
Multi-image photography of the motion of the pucks on the air table can be obtained by illuminating the air table with a stroboscopic lamp.

(For the elastic collision)

Puck A was launched at Puck B (initially stationary)
A program was used to obtain the motion of the pucks at different time intervals in coordinates scaled to metres.
Strobe was set a 6 flashes per second, so the time interval between each image (coordinate points) was 1/6 of a second.

Now the annoying part......
the analysis wants a graph of momentum against time of each puck on the same axes
Puck A has a nice slope, momentum is increasing and then hits Puck B and starts decreasing cause momentum must be conserved.
it looks weird cause the puck B is initially stationary, so for the first 3 time intervals it is 0 and then goes up.
So now we state a relationship between momenta before and momenta after judging by the graph shapes.

Anyways, the next step is to adjust quantities of the graph to somehow show that momentum is conserved (of course some error will be present) so somehow get a relationship or two things for before and after, which when compared will be very close and hence momentum conserved.

Oh and so far i have tried a bunch of things but this one seemed the least wrong m*delta(s) vs time


« Last Edit: October 07, 2014, 11:11:43 pm by qwerty04 »

silverpixeli

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Re: VCE Physics Question Thread!
« Reply #635 on: October 08, 2014, 12:17:55 am »
+1
i think you should be graphing total momentum vs time and showing that it's constant.

total momentum will be the sum of the momenta of the two pucks, i.e. m1 v1 + m2 v2 which should remain the same across the collision


sounds like a pretty epic prac though, stroboscopes!
« Last Edit: October 08, 2014, 12:22:56 am by silverpixeli »
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Re: VCE Physics Question Thread!
« Reply #636 on: October 08, 2014, 07:49:24 am »
0
Hi everyone

Just did 2006 VCAA, and I found motion section so hard, much harder than any neap, insight etc commercial exam motion section. How is everyone else feeling about motion 06? Will the motion section be of that difficulty in 14? Does the difficulty stay the same from 06-13?

thanks
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Re: VCE Physics Question Thread!
« Reply #637 on: October 08, 2014, 09:23:35 am »
+2
Hi everyone

Just did 2006 VCAA, and I found motion section so hard, much harder than any neap, insight etc commercial exam motion section. How is everyone else feeling about motion 06? Will the motion section be of that difficulty in 14? Does the difficulty stay the same from 06-13?

thanks

based on grade distributions that paper was the hardest one evar, A+ cutoff was 79% for unit 3 2006 and 0 people got full marks

all unit 3 and 4 exams except that from 2004-2012 have A+ cutoffs between 85% and 96% with the years towards 85% being considered the harder papers (they try to go for ~90%) (with the exception of unit 3 2004 which was 81%) (I havent added 2013 because this is my stats from last year)

should be fine!
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Re: VCE Physics Question Thread!
« Reply #638 on: October 08, 2014, 04:09:19 pm »
0
based on grade distributions that paper was the hardest one evar, A+ cutoff was 79% for unit 3 2006 and 0 people got full marks

all unit 3 and 4 exams except that from 2004-2012 have A+ cutoffs between 85% and 96% with the years towards 85% being considered the harder papers (they try to go for ~90%) (with the exception of unit 3 2004 which was 81%) (I havent added 2013 because this is my stats from last year)

should be fine!
Thank god.

I did so many commercial exams, and thinking I would now be able to ace VCAA, I did 2006 and got so freaking depressed haha. Would you reccomend me going over all those questions? Can they come up?

Thanks
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Re: VCE Physics Question Thread!
« Reply #639 on: October 08, 2014, 09:09:34 pm »
0
based on grade distributions that paper was the hardest one evar, A+ cutoff was 79% for unit 3 2006 and 0 people got full marks

all unit 3 and 4 exams except that from 2004-2012 have A+ cutoffs between 85% and 96% with the years towards 85% being considered the harder papers (they try to go for ~90%) (with the exception of unit 3 2004 which was 81%) (I havent added 2013 because this is my stats from last year)

should be fine!

How can you tell how many people got full marks for particular exams

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Re: VCE Physics Question Thread!
« Reply #640 on: October 08, 2014, 09:28:45 pm »
0
How can you tell how many people got full marks for particular exams
Usually it says in the assessors report. For the 2013 one it didnt, but for years like 2009 where 100s and 100s people got 100% they did
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silverpixeli

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Re: VCE Physics Question Thread!
« Reply #641 on: October 08, 2014, 10:57:51 pm »
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How can you tell how many people got full marks for particular exams

Yes some older physics/specialist reports seemed to have this information, but I'm going based off the spreadsheet that my physics teacher gave me towards the end of last year which was his info on grade distributions and everything so idk he may have gotten the information from some other source related to being a VCE physics teacher. he had all sorts of info like that.
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Re: VCE Physics Question Thread!
« Reply #642 on: October 08, 2014, 10:59:54 pm »
0
can someone please help me with this question?

I guess im stuck between those three big words: weight = mg
weightlessness? - whats that?
aparent weightlessness - when normal = 0?

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Re: VCE Physics Question Thread!
« Reply #643 on: October 08, 2014, 11:43:29 pm »
+1
can someone please help me with this question?

I guess im stuck between those three big words: weight = mg correct, force due to gravity
weightlessness? - whats that? actually having weight = 0, i.e. m=0 or g=0, doesnt truly happen at any times here
aparent weightlessness - when normal = 0 yep

so 1.8g refers to the gravitational force the plane 'feels' even though the actual force on it is always based on g. it's to do with apparent weight. near the start and end of the maneuver the plane is in the bottom half of a vertical circular path and the force on the wings towards the centre of this circle is kinda the normal force from the air, providing this greater force.
same story with zero g, apparent weightlessness because there is no normal force as the plane is at the top of another vertical circle, its weight force is all that is needed to cause circular motion.
at all times the weight of the plane is unchanged and it is not truly weightless because weight is not zero.

dont think you'd need to talk about circles because that's not what it asked for, i just mentioned it to help explain!
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Re: VCE Physics Question Thread!
« Reply #644 on: October 08, 2014, 11:46:58 pm »
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Where would you find the A+ cutoffs and things like that on the vcaa website for physics