HSC Physics Marathon 2013-2015 Archive (2 Viewers)

[funnytomato]

re: HSC Physics Marathon Archive

You all are misinterpreting the Newton question!

It says for the period AFTER the rocket burn was completed. You should not mention ANYTHING about expulsion of gases as this would be DURING the rocket burn

What do you think of the notes from the marking centre, which states:

In better responses, candidates were able to describe and relate two or more of Newton's Laws of
Motion in words and/or equations to the return trip of Apollo 13, ie the period after leaving the
lunar orbit.
In weaker responses, candidates incorrectly applied the slingshot effect to the motion of the rocket
around the moon.

I just fail to see how we can use 2 or all 3 of Newton's Laws of Motion if no energy from the engine is involved/should be mentioned.

After leaving the lunar orbit, worked is done to put it back into free return trajectory.

Then after that , NLUG seems to be the most important thing when it is in the free-return trajectory, rather than any of the Laws of Motion.

 

[funnytomato]

re: HSC Physics Marathon Archive

It's quite a difficult question! Essentially, it wants you to justify the statement made by Jim Lovell, in order to do this, you must explain how Newtons Laws apply to the motion of the craft after the rockets engines are extinguished.

Also what exactly are Newton's Laws of Motion? in particular for HSC physics

It sounds 'trivial' but I guess most of us do not really know what they actually are.

 

[Rhinoz8142]

re: HSC Physics Marathon Archive

Also what exactly are Newton's Laws of Motion? in particular for HSC physics

It sounds 'trivial' but I guess most of us do not really know what they actually are.

Is just the 3 laws,
1) an object either remains at rest or continues to move at a constant velocity, unless acted upon by an external force
2) F=M.A where force is equal by the multiple of mass x acceleration
3) Every action had an opposite (same magnitude ) reaction.

 

[PhysicsMaths]

re: HSC Physics Marathon Archive

Next Question:
The Michelson-Morley experiment attempted to measure the relative velocity of the Earth through the aether.
a) Explain why the Earth was believed to be travelling through the aether (2 marks)
b) Evaluate the effect that the result of the M-M experiment had on scientific thinking at the time (3 marks)

 

[Kaido]

re: HSC Physics Marathon Archive

a)It was previously (possibly between the mid-17th and late 19th Century) thought that energy required a medium for transmission and propagation. Having concluded that light moves as a waveform - physicists inferred from other wave motions to better understand light. Others known – including sound waves, water waves and earthquake waves; all required a medium through which to travel. And so it was believed that light would also require a medium. (However, no such medium was found)
b)M&M led to... Einstein (believing in the unity of physics) postulated that:
-The laws of physics are the same in all frames of reference (that is, the principle of relativity always holds)
-The speed of light in empty space is always the same value - c (3x108m/s), which is independent of the motion of the observer
-The aether was superfluous and is no longer needed to explain the behaviour of light

Edit: Will re-do b) later, as I'm playing LoL atm

 

[Kaido]

re: HSC Physics Marathon Archive

An observer on Earth watches two spaceships. According to their measurements, spaceship A is travelling away from Earth at 0.5c, and spaceship B is approaching Earth at 0.75 c. How fast is spaceship A moving according to the crew on spaceship B?

Not yet solved (Anyone can answer it this time)

 

[InteGrand]

re: HSC Physics Marathon Archive

Not yet solved (Anyone can answer it this time)

We don't know the directions spaceship A and B are moving in; the answer will depend on this.

 

[Kaido]

re: HSC Physics Marathon Archive

We don't know the directions spaceship A and B are moving in; the answer will depend on this.

One is moving away, one is approaching o-o (2D only, no angles etc.)

sadly not 3D Integrand, would make the problem slightly more interesting

 

[Fizzy_Cyst]

re: HSC Physics Marathon Archive

Not yet solved (Anyone can answer it this time)

Should be ~0.91c

 

[Fizzy_Cyst]

re: HSC Physics Marathon Archive

Not yet solved (Anyone can answer it this time)

Should be ~0.91c

 

[Fizzy_Cyst]

re: HSC Physics Marathon Archive

What do you think of the notes from the marking centre, which states:



I just fail to see how we can use 2 or all 3 of Newton's Laws of Motion if no energy from the engine is involved/should be mentioned.

After leaving the lunar orbit, worked is done to put it back into free return trajectory.

Then after that , NLUG seems to be the most important thing when it is in the free-return trajectory, rather than any of the Laws of Motion.

Hey funnytom,

I would suggest that using N1L, you could say something along the lines of 'seeing as the velocity of the craft is towards the Earth, then according to N1L, in the absence of a net force it will continue to move towards the Earth.' Then say 'however, there is a net force, which is provided by gravity and according to N2L this causes the craft to accelerate towards the Earth.' You could then go on to say 'according to N3L, the craft also exerts a gravitational force on the Earth, but the effect is unnoticeable, due to the far greater mass of the Earth compared to the craft'

I'd build my response around that

 

[Fizzy_Cyst]

re: HSC Physics Marathon Archive

What do you think of the notes from the marking centre, which states:



I just fail to see how we can use 2 or all 3 of Newton's Laws of Motion if no energy from the engine is involved/should be mentioned.

After leaving the lunar orbit, worked is done to put it back into free return trajectory.

Then after that , NLUG seems to be the most important thing when it is in the free-return trajectory, rather than any of the Laws of Motion.

Hey funnytom,

I would suggest that using N1L, you could say something along the lines of 'seeing as the velocity of the craft is towards the Earth, then according to N1L, in the absence of a net force it will continue to move towards the Earth.' Then say 'however, there is a net force, which is provided by gravity and according to N2L this causes the craft to accelerate towards the Earth.' You could then go on to say 'according to N3L, the craft also exerts a gravitational force on the Earth, but the effect is unnoticeable, due to the far greater mass of the Earth compared to the craft'

I'd build my response around that

 

[InteGrand]

re: HSC Physics Marathon Archive

One is moving away, one is approaching o-o (2D only, no angles etc.)

I assume you mean 1D (i.e. motion in a straight line only).

Even still, it depends whether the spaceships are travelling in the same direction or not (are the spaceships heading for a head-on collision, or are they moving in the same direction?).

And this question can't be done using HSC Physics knowledge alone, since vector addition in special relativity is outside the syllabus (and not as simple as vector addition in Galilean relativity).

 

[Kaido]

re: HSC Physics Marathon Archive

I assume you mean 1D (i.e. motion in a straight line only).

Even still, it depends whether the spaceships are travelling in the same direction or not (are the spaceships heading for a head-on collision, or are they moving in the same direction?).

And this question can't be done using HSC Physics knowledge alone, since vector addition in special relativity is outside the syllabus (and not as simple as vector addition in Galilean relativity).

it may be outside the physics syllabus, but a little trig or calculus doesn't hurt.
And yes, the spaceships are moving 'head on' (though they obv don't collide and explode...)

 

[Kaido]

re: HSC Physics Marathon Archive

I assume you mean 1D (i.e. motion in a straight line only).

Even still, it depends whether the spaceships are travelling in the same direction or not (are the spaceships heading for a head-on collision, or are they moving in the same direction?).

And this question can't be done using HSC Physics knowledge alone, since vector addition in special relativity is outside the syllabus (and not as simple as vector addition in Galilean relativity).

it may be outside the physics syllabus, but a little trig or calculus doesn't hurt (or a good imagination)
And yes, the spaceships are moving 'head on' (though they obv don't collide and explode...)

 

[InteGrand]

re: HSC Physics Marathon Archive

it may be outside the physics syllabus, but a little trig or calculus doesn't hurt.
And yes, the spaceships are moving 'head on' (though they obv don't collide and explode...)

Well, the formula for relative velocity in 1D in Special relativity is

(so you can see that relative speed is always between -c and +c for 0

and subsituting u = 0.5c and v = 0.75 c, answer is approx. 0.91c.

However, deriving the Lorentz transformations is not trivial (is that what you were looking for?).

 

[Kaido]

re: HSC Physics Marathon Archive

Pretty much (For high high school level anyway)

 

[Fizzy_Cyst]

re: HSC Physics Marathon Archive

New Question:

Beginning with the Law of Universal gravitation, derive a formula that can be used to calculate the approximate radius of the Earth using data provided on your formula/data sheet. Calculate this value.

NB: If you EVER need to use radius of the Earth in a question, but are not given it, use this method to figure it out -- don't just plug in a 'generally accepted' value, I see this being used as a discriminator in a part of a question in the future some time

 

[Kaido]

re: HSC Physics Marathon Archive

F(g)=GM1M2/r^2

G=6.67x10^-11 m^3kg^-1s^-2
M of earth=5.97x10^24kg

edit: brb, i misread question lol

 

[Fizzy_Cyst]

re: HSC Physics Marathon Archive

F(g)=GM1M2/r^2

G=6.67x10^-11 m^3kg^-1s^-2
M of earth=5.97x10^21kg
Radius of earth=~6378km

(dont have formula sheet, no clue what exact values are)

por que?

How did you arrive at your asnwer for 'r'?