HSC Physics Marathon 2013-2015 Archive (1 Viewer)

[Kaido]

re: HSC Physics Marathon Archive

r^3/t^2=r^3/t^2
sub in values for earth and mercury. rearrange to get period then square root. ggwp

if u used GM/4pi^2 i dont think it works. correct me if im wrong, but that is a constant specific to earth, no?

 

[anomalousdecay]

re: HSC Physics Marathon Archive

Ok a few people are getting confused about length, time and mass dilation.

I'll give an example questions. Once answered, please post another question around this topic.

A person sits on a train moving at 0.90c relative to a platform. An observer is standing still at the platform. The boy on the train observes the train to be 50 m long and 5000 kg in mass. The train takes 10.0^(-12) seconds to pass the platform relative to the person sitting on the train. Also, the person on the platform also has a stopwatch. This stopwatch is started and stopped after exactly 1.0 seconds. The bench on the platform, as measured by the person on the platform, is 100 kg in mass and 2.0 m wide.

Calculate:

a) The relative mass of the train observed by the observer on the platform.
b) The relative length of the train observed by the observer on the platform.
c) The relative time observed by the person on the platform for the train to pass the platform.
d) The relative time observed by the person on the train for that one second to tick on the stopwatch at the platform.
e) The relative mass of the bench on the platform as observed by the person on the train.
f) The relative width of the bench on the platform as observed by the person on the train.

 

[x1]

re: HSC Physics Marathon Archive

Question: Pure Germanium can be doped by adding small amounts of phosphorus.

a) is doped germanium an n-type or p-type semiconductor. Justify your answer.
b) explain how the addition of phosphorus alters the electrical conductivity of germanium

need help asap, i don't do chem

 

[Drsoccerball]

re: HSC Physics Marathon Archive

Question: Pure Germanium can be doped by adding small amounts of phosphorus.

a) is doped germanium an n-type or p-type semiconductor. Justify your answer.
b) explain how the addition of phosphorus alters the electrical conductivity of germanium

need help asap, i don't do chem

Which module is this ?... so far our class has done space and just finished motors

 

[astroman]

re: HSC Physics Marathon Archive

Which module is this ?... so far our class has done space and just finished motors

http://hsc.csu.edu.au/physics/core/implementation/9_4_3/943net.html

 

[astroman]

re: HSC Physics Marathon Archive

Question: Pure Germanium can be doped by adding small amounts of phosphorus.

a) is doped germanium an n-type or p-type semiconductor. Justify your answer.
b) explain how the addition of phosphorus alters the electrical conductivity of germanium

need help asap, i don't do chem

a) n-type since it has 5 valence electrons, there are more negative charge carriers than positive holes.
b) if a semiconductor is doped with phosphorus then extra electrons are added and this increases the conductivity.

 

[Kaido]

re: HSC Physics Marathon Archive

a) 11470.8kg
b)21.79m
c)2.29x10^-12 s
d) 2.29s
e) 229.4kg
f) 0.872m

 

[anomalousdecay]

re: HSC Physics Marathon Archive

a) 11470.8kg
b)21.79m
c)2.29x10^-12 s
d) 2.29s
e) 229.4kg
f) 0.872m

I got the same for those. Post a question up.

 

[Kaido]

re: HSC Physics Marathon Archive

I've asked 4-5 of my friends to try those relativity questions you posted anom. Most got the first three OR the last three correct. I think what confused them was t(0),m(0),l(0).
Those variables with a (0) means "proper", so the actual length, mass, time without it being in motion. Someone should try and explain this concept

 

[photastic]

re: HSC Physics Marathon Archive

I've asked 4-5 of my friends to try those relativity questions you posted anom. Most got the first three OR the last three correct. I think what confused them was t(0),m(0),l(0).
Those variables with a (0) means "proper", so the actual length, mass, time without it being in motion. Someone should try and explain this concept

I just cheated, if i'm finding the relativistic time or mass, my answer has to be greater than the given time whereas my answer must be smaller if finding the rest time or mass. It is the opposite for length.

 

[Rhinoz8142]

re: HSC Physics Marathon Archive

I miss physics :'(

 

[anomalousdecay]

re: HSC Physics Marathon Archive

I've asked 4-5 of my friends to try those relativity questions you posted anom. Most got the first three OR the last three correct. I think what confused them was t(0),m(0),l(0).
Those variables with a (0) means "proper", so the actual length, mass, time without it being in motion. Someone should try and explain this concept

Yeah I'm not the best at explaining this but:

You might find this helpful.

http://newt.phys.unsw.edu.au/einsteinlight/jw/module4_time_dilation.htm

I'm still unsure how to explain it myself because I usually just look at it and do the question based on what is what. Time will always seem to tick slower for the spacecraft iff the observer at rest is seeing it (that was a bad and possibly confusing explanation by me oops).

I think the best explanation I can think of is that t_o is the observed time in the observed reference frame (so we take this as the frame that is being defined at rest) and t_v is the observed time in one frame in reference to the other (the one which we say is moving relative to the one we chose to be at rest from the question).

This also is the same for length and mass dilation.

If you ever forget: faster --> shorter in length, slower clock ticks and heavier mass relative to a frame of reference at rest. Then you can apply that to the formula to remember what is what.

And in this thread http://community.boredofstudies.org/263/space/334622/time-dilation-confusion-s.html

 

[superstar12]

re: HSC Physics Marathon Archive

Can someone explain why the answer is C, not B?

 

[astroman]

re: HSC Physics Marathon Archive

Can someone explain why the answer is C, not B?

View attachment 31826

eddy currents, there is a break in the disks so the current is field is temporarily lost allowing it to fall faster lost, i'm not sure of the answer, I was initially thinking it would be P and Q arrive simultaneolusy and R first

 

[Kaido]

re: HSC Physics Marathon Archive

Can someone explain why the answer is C, not B?

View attachment 31826

I see where you're coming from. We can't technically examine the strength of the eddy-currents produced in P and R, since one is an insulator and the other has a break that reduces the size of the potential eddy-c. (I reckon there's a flaw in this question)
Q would obviously arrive last

eddy currents, there is a break in the disks so the current is field is temporarily lost allowing it to fall faster lost, i'm not sure of the answer, I was initially thinking it would be P and Q arrive simultaneolusy and R first

How did you come to this conclusion?

 

[Drsoccerball]

re: HSC Physics Marathon Archive

I thought it was B aswell

 

[someth1ng]

re: HSC Physics Marathon Archive

Physically, the correct answer is B but in HSC, if there's a slit, the correct answer is "no eddy currents are produced" and hence, the answer becomes C. Obviously, in real physics, the correct answer should be B.

 

[Drsoccerball]

re: HSC Physics Marathon Archive

Physically, the correct answer is B but in HSC, if there's a slit, the correct answer is "no eddy currents are produced" and hence, the answer becomes C. Obviously, in real physics, the correct answer should be B.

So if theres a slit no eddy currents are produced ?

 

[astroman]

re: HSC Physics Marathon Archive

So if theres a slit no eddy currents are produced ?

no, they are interrupted

 

[Drsoccerball]

re: HSC Physics Marathon Archive

Explain how the galvanometer and the loudspeaker works.