HSC Physics Marathon 2013-2015 Archive (3 Viewers)

[PhysicsMaths]

re: HSC Physics Marathon Archive

Having a look at the question, where it says it takes 3s to go a further 4m, that impossible assuming g =-9.8ms^-2.

I get no real solutions for g =-9.8! Show me working!

I am able to get the 9.1m, but that involves an algebraic mistake.

Are you sure it is not 0.3s or something?

Yeah, I was having the same problem. I tried multiple approaches but they ended up contradicting each other

 

[InteGrand]

re: HSC Physics Marathon Archive

Logically makes no sense. You can't have a frictionless plane and expect to achieve constant velocity.

Oh and what is the 'normal force'?

(Hella bad at english as u can tell)

Sorry again, didn't read his problem statement thoroughly.

So yes, there is friction, must be equal to the force due to gravity acting down the plane.

And normal force in physics is the force the plane exerts on the object in a direction perpendicular to the plane ("normal" means perpendicular in geometry). ( http://en.wikipedia.org/wiki/Normal_force )

(Normal in geometry: http://en.wikipedia.org/wiki/Normal_(geometry) )

 

[Kaido]

re: HSC Physics Marathon Archive

Haha, thanks for clearing that up
(I thought 'normal' as in 'typical')

Right, so from my prelim knowledge: F(perp)=5x9.8xcos30

(But that doesnt explain where the 2m/s fits into the picture, because that's a parallel force)

 

[PhysicsMaths]

re: HSC Physics Marathon Archive

Not sure if the current question has been answered, but here's another one:
Parts of a space mission involve a spacecraft spending time in geostationary orbit, and then returning safely to Earth.
Analyse the forces acting on this spacecraft during these parts of the mission.

 

[Kaido]

re: HSC Physics Marathon Archive

Not sure if the syllabus directly addresses the dangers of being in space (e.g. possibility of mass decrease due to osteopenia which is from weightlessness)
As for forces during re-entry:
-> gravitational acceleration in combination with spacecraft acceleration -> F=ma (mass remains constant), so Force proportionally increases as accel. increases
This means the g-force experienced will definitely be ******* high

 

[anomalousdecay]

re: HSC Physics Marathon Archive

Don't need to know about osteopenia.

 

[Kaido]

re: HSC Physics Marathon Archive

Next question plz

 

[PhysicsMaths]

re: HSC Physics Marathon Archive

Hints? What syllabus dot points does this reference in particular?

In your response you should refer to the forces acting on the spacecraft. What is the main force acting on it to maintain a stable orbit? What are the forces it experiences during re-entry, and how does that effect the motion of the spacecraft? (Taken from marker's notes)

6 mark question btw

 

[Kaido]

re: HSC Physics Marathon Archive

The forces on a spacecraft in stable orbit? (I Thought spacecraft travel to end of the universe, rofl)

If so, then the forces are the centripetal force (due to angular constant velocity and gravitational attraction). In a geostationary orbit, the angular velocity is perp. (i.e. tangent) to the orbit, whilst the gravitational attraction acts downwards.

In re-entry, gravitational acceleration in combination with spacecraft acceleration -> F=ma (mass remains constant), so Force proportionally increases as accel. increases. This means the g-force experienced by the astronauts will be quite high (though on-board equipment and spacecraft design will ensure the g-load does not exceed unsafe levels e.g. safety harness and specially designed sofas?)
Spacecraft also experiences a compressive force as well as air resistance -> causing heat up which is a result of the conversion of forces: from kinetic energy -> heat energy

(For 6 marks, i reckon this question is quite ambiguous. So there could be a range of other things to talk about also)

Edit: I edited the response to hopefully answer the question as I would exam-style

 

[jyu]

re: HSC Physics Marathon Archive

Not sure what you're looking for.
Frictional force, gravitational force, Perp. force, Parallel force ???

The reaction force as in Newton's third law.

 

[Fizzy_Cyst]

re: HSC Physics Marathon Archive

The forces on a spacecraft in stable orbit? (I Thought spacecraft travel to end of the universe, rofl)
If so, then the forces are the centripetal force (due to angular constant velocity and gravitational attraction). In a geostationary orbit, the angular velocity is perp. (i.e. tangent) to the orbit, whilst the gravitational attraction acts downwards.

In re-entry (which i already partially mentioned), spacecraft experiences a compressive force + air resistance -> causing heat up (conversion of forces, which i cbb detailing).

For 6 marks, i reckon this question is quite ambiguous. So there could be a range of other things to talk about also

Answer it the way you would in an examination! That is the only way you will gain valuable feedback cuz if you cbb answering the question completely, I (and presumably, others) cbb giving feedback and any feedback given will not be valuable as it is not an 'examination' response!!

That is the only way we can see where you need help. Trust me, most students cannot structure an analyse response correctly, it is a very difficult verb

 

[Kaido]

re: HSC Physics Marathon Archive

Answer it the way you would in an examination! That is the only way you will gain valuable feedback cuz if you cbb answering the question completely, I (and presumably, others) cbb giving feedback and any feedback given will not be valuable as it is not an 'examination' response!!

That is the only way we can see where you need help. Trust me, most students cannot structure an analyse response correctly, it is a very difficult verb

Ohh, I thought we answered questions to help others structure their own responses.

(I edited my response above)

 

[Fizzy_Cyst]

re: HSC Physics Marathon Archive

Ohh, I thought we answered questions to help others structure their own responses.

I see it being beneficial both ways. Others can read your responses and hopefully gain some insight, likewise, feedback can be given to you if there are areas of your own response lacking in sufficient detail or misconceptions etc.. They have ultimately been the biggest downfall in this marathon thread over the years, no one really gives feedback and sometimes answers aren't given to the extent they would be in an examination. A question is answered and then it goes straight on to the next question without any 'marking' or 'peer feedback' etc..

Treat it like your homework if your teacher was marking it, that way you will get constructive feedback and it is a much more valid way of determining your areas of weakness, particularly for those 4-6 markers.

 

[PhysicsMaths]

re: HSC Physics Marathon Archive

next question:
http://imgur.com/yUVJX3R (I like this one because of the diagram)
a) determine the maximum height reached above the ground by the projectile (1 mark)
b) does the projectile have the correct range to hit the wall? justify your answer using relevant calculations (3 marks)

 

[Kaido]

re: HSC Physics Marathon Archive

Hit what part of the wall? (Quite a vague question I reckon)

 

[Kaido]

re: HSC Physics Marathon Archive

a)29.8m
b)No. t=4.76, Range only reaches ~137.8m

 

[InteGrand]

re: HSC Physics Marathon Archive

lol Q.19 from the 2005 HSC Physics paper (4 marks):

"In 1970 NASA launched Apollo 13, their third mission planned to land humans on the Moon. Half-way to the Moon a huge explosion crippled the spacecraft. The only way home for the astronauts was to fly around the back of the Moon and then fire the rocket engine to take the craft out of lunar orbit and put it into an Earth-bound trajectory.

At the completion of the rocket engine burn, mission leader Jim Lovell was heard to say, ‘We just put Isaac Newton in the driver’s seat’.
Given that the spacecraft returned safely to Earth, justify Jim Lovell’s statement."

 

[Rhinoz8142]

re: HSC Physics Marathon Archive

lol Q.19 from the 2005 HSC Physics paper (4 marks):

"In 1970 NASA launched Apollo 13, their third mission planned to land humans on the Moon. Half-way to the Moon a huge explosion crippled the spacecraft. The only way home for the astronauts was to fly around the back of the Moon and then fire the rocket engine to take the craft out of lunar orbit and put it into an Earth-bound trajectory.

At the completion of the rocket engine burn, mission leader Jim Lovell was heard to say, ‘We just put Isaac Newton in the driver’s seat’.
Given that the spacecraft returned safely to Earth, justify Jim Lovell’s statement."

Omg, I remember this question..I did it so many times that I memorized my answer..


But I am gonna see if any of the 2015er can solve it

 

[Kaido]

re: HSC Physics Marathon Archive

No clue what the question is asking.
And how does the spacecraft survive after getting hit?

'We just put Isaac Newton in the driver’s seat’ - is this a metaphor for something?

 

[InteGrand]

re: HSC Physics Marathon Archive

'We just put Isaac Newton in the driver’s seat’ - is this a metaphor for something?

Looks like it.