HSC Physics Marathon 2013-2015 Archive (1 Viewer)

[someth1ng]

re: HSC Physics Marathon Archive

Altitude is not the only factor affecting acceleration due to gravity, its value is also affected by:
Earth's Rotations-Creates a centrifugal effect at the equator slightly lowering the value of g
Thickness of Earth's Crust-Varies and contains dense mineral deposits and tectonic plate boundaries which alter the value of g
Earths Shape-The earth is not a perfect sphere but is slightly flatter at the poles-->Thus the value of g is slightly higher at the poles (closer to the centre of the earth)
All these factors contribute to the value of g, thus simply assuming the relative value of g at a particular location based upon one criteria (ie altitude) does not necessarily hold.

A rote learned answer which doesn't really answer the question - you didn't even mention Mount Everest.

1. The rotation should make the value of g at Everest even lower and the thickness of the crust, itself, isn't a good reason if you don't elaborate on it further.
2. It's better to say that Earth is not uniformly dense so certain parts of the planet will be more dense, increase the value of g in those areas and areas where it's less dense will have lower values of g.
3. Again, with your last reason, Everest is closer to the equator than it is to the poles - you need to elaborate on it and say that there's other mountains near the equator.

I would like to add a last reason is that the Everest is the highest point above sea level but it isn't necessarily the most distant point from the centre of the Earth because the slight bulge makes other smaller mountains further from the centre of the Earth, making their value of g lower.

If this was a 4 mark question, I'd give you 0 or 1, at best.

 

[JJ345]

re: HSC Physics Marathon Archive

A rote learned answer which doesn't really answer the question - you didn't even mention Mount Everest.

1. The rotation should make the value of g at Everest even lower and the thickness of the crust, itself, isn't a good reason if you don't elaborate on it further.
2. It's better to say that Earth is not uniformly dense so certain parts of the planet will be more dense, increase the value of g in those areas and areas where it's less dense will have lower values of g.
3. Again, with your last reason, Everest is closer to the equator than it is to the poles - you need to elaborate on it and say that there's other mountains near the equator.

I would like to add a last reason is that the Everest is the highest point above sea level but it isn't necessarily the most distant point from the centre of the Earth because the slight bulge makes other smaller mountains further from the centre of the Earth, making their value of g lower.

If this was a 4 mark question, I'd give you 0 or 1, at best.

yeah my answer was pretty terrible Thanks a lot for your feedback =)

 

[fionarykim]

re: HSC Physics Marathon Archive

There doesnt seem to be another Question so heres a question! someone answer it
-Apply Keplers 3rd Law and conservation of momentum to explain why gravitational slingshot maneuvers increase the speed of space probes.

 

[abdog]

re: HSC Physics Marathon Archive

HSC 05 Q5:
Napoleon attacked Moscow in 1812 with his cannon firing a shot at an elevation angle of 45 degrees. Napoleon then decided to fire a second shot at the same speed but at an elevation angle of 50 degrees. Which of the following observations would Napoleon expect to be true about the second shot when compared with the first?

A.Larger range
B.Shorter range
C.Longer time of flight
D.Shorter time of flight

 

[JJ345]

re: HSC Physics Marathon Archive

HSC 05 Q5:
Napoleon attacked Moscow in 1812 with his cannon firing a shot at an elevation angle of 45 degrees. Napoleon then decided to fire a second shot at the same speed but at an elevation angle of 50 degrees. Which of the following observations would Napoleon expect to be true about the second shot when compared with the first?

A.Larger range
B.Shorter range
C.Longer time of flight
D.Shorter time of flight

C-Longer time of flight (increasing angle of elevation increases vertical component of velocity)

 

[abdog]

re: HSC Physics Marathon Archive

C-Longer time of flight (increasing angle of elevation increases vertical component of velocity)

Yeah but wouldnt A work as well? Seeing as the angle was increased, thus the shot can travel further before hitting the ground?

 

[JJ345]

re: HSC Physics Marathon Archive

Yeah but wouldnt A work as well? Seeing as the angle was increased, thus the shot can travel further before hitting the ground?

Did you copy the question down wrong by any chance? Is it supposed to be 40 then 50 degrees angle of elevation-->Then there would be identical range as the are both +5 or -5 degrees from 45 degrees.

 

[Menomaths]

re: HSC Physics Marathon Archive

it's 40

 

[abdog]

re: HSC Physics Marathon Archive

Did you copy the question down wrong by any chance? Is it supposed to be 40 then 50 degrees angle of elevation-->Then there would be identical range as the are both +5 or -5 degrees from 45 degrees.

Sorry! its 40. But still, what does 45 degrees have to do with this? The book says its maximum but I dont understand what it means by that

 

[JJ345]

re: HSC Physics Marathon Archive

Sorry! its 40. But still, what does 45 degrees have to do with this? The book says its maximum but I dont understand what it means by that

I'll try explain it algebraically,
y = utsina - ½ gt2 (1)
x = utcosa (2)
When the particle returns to the ground, y = 0. Substituting this into (1):

0 = utsina - ½ gt2
t (usina - ½ gt) = 0
t = 0 or t = 2usina/g (3)
Therefore when x = Range, t = 2u sina / g
Substituting into (2)
Range = ucosa (2usina)/g
=u2sin2a/g
Now when a=40 or a=50 we get identical range since sin100=sin80 while u and g are constant
Also when a=45 sin2a=1 (its max value)-->Thus max range.

I hope that makes sense.
Sorry its pretty ugly, I don't know how to use latex.

 

[Fizzy_Cyst]

re: HSC Physics Marathon Archive

Note that 45 degrees is only max range if there's no change in y displacement! I.e., starts on ground, finishes on ground

 

[Fizzy_Cyst]

re: HSC Physics Marathon Archive



2 questions.

1: determine the gravitational force acting on the probe at its current location.

2: determine the distance away from Saturn which it must be in order to experience no NET gravitational force

 

[Menomaths]

re: HSC Physics Marathon Archive

View attachment 28796

2 questions.

1: determine the gravitational force acting on the probe at its current location.

2: determine the distance away from Saturn which it must be in order to experience no NET gravitational force

Is 2 infinite distance?

 

[Fizzy_Cyst]

re: HSC Physics Marathon Archive

Sorry, should have specified! The craft is between Jupiter and Saturn for Q2. So, nope, not at infinity

 

[superSAIyan2]

re: HSC Physics Marathon Archive

is 1) 1.03 x 10^-3 N towards Jupiter's centre

 

[superSAIyan2]

re: HSC Physics Marathon Archive

and is 2, 1.16 x 10^11 m from Saturns centre

 

[Fizzy_Cyst]

re: HSC Physics Marathon Archive

1 is correct
2 is incorrect

 

[nerdasdasd]

re: HSC Physics Marathon Archive

 

[Menomaths]

re: HSC Physics Marathon Archive

b?

 

[nerdasdasd]

re: HSC Physics Marathon Archive

b?