Prelim Physics Thread (3 Viewers)

[Green Yoda]

But thanks for the reply, appreciate it
I might reword it

 

[Nailgun]

tbh I agree with jathu, you should still explicitly use the terms critical angle and angle of incidence in your answer

 

[Green Yoda]

Thanks for the advice
I'll reword it and post it here later

 

[AfroNerd]

Hi guys, I'm unsure about how to do this circular motion question:

Calculate the gravitational force acting on earth if earth orbits the sun at 145 million km and has a mass of 6x10^23kg.

 

[leehuan]

Hi guys, I'm unsure about how to do this circular motion question:

Calculate the gravitational force acting on earth if earth orbits the sun at 145 million km and has a mass of 6x10^23kg.

Is this really preliminary physics...

Also, I am 100% sure that the mass of the Earth is 6.0*10²⁴ not to the 23rd.

Unless you were meant to say 145 million kilometers per second and not just km.

 

[AfroNerd]

Yeah sorry I meant 6.0x10^24 and the question says at a distance of 145km.

 

[leehuan]

Had a re-think about it. In the HSC course this is much more easily done but the approach can be done using multiple formulae from preliminary physics.

Note that 145 million km = 145 billion metres





Then plug straight into F_c=mv²/r

 

[AfroNerd]

okay thanks heaps, and just wondering if the gravitational force is the same as the centripetal force

 

[leehuan]

okay thanks heaps, and just wondering if the gravitational force is the same as the centripetal force

Yes. In the HSC course you will find out that the pull of gravity is effectively what forces the Earth to undergo it's circular motion. But the fact it has an orbital velocity explains why the Earth doesn't fall into the sun

 

[porcupinetree]

okay thanks heaps, and just wondering if the gravitational force is the same as the centripetal force

It's more correct to say that the gravitational force supplies a centripetal force, allowing the orbiting object to undergo circular motion.

(Note: (I'm not accusing you of this necessarily but it might help) it's a very common trap for students to think that when an object is undergoing circular motion (eg when in orbit), there is some extra force called the 'centripetal force' which acts on the object and causes its circular motion. This thinking is wrong - what actually happens is, the sum of all the forces acting upon the body will lead to a net force on the body, and if this force is perpendicular to the object's direction of motion, then this net force is called the centripetal force, and the object will begin to undergo circular motion.)

 

[Green Yoda]

For the following dot point I have discussed GPS. Can you see if my answer is good or not and what to add/remove from it?

• Identify data sources, gather, process and present information from secondary sources to identify areas of current research and use the available evidence to discuss some of the underlying physical principles used in one application of physics related to waves, such as:
– Global Positioning System
– CD technology
– The internet (digital process)
– DVD technology

Global Positioning System:
The GPS is made up of 24 satellites orbiting the Earth at 17,600km altitude. They are positioned in a way that the entire surface of the Earth has a line of sight between a couple of the satellites. The line of sight connection allows it to locate your position on Earth. The satellites are in conjunction to a series of ground stations which are in constantly in contact with the satellites via radio communication and manipulate the satellites movements.

The GPS are outfitted with Atomic clocks that are made up of cesium. These clocks tell precise time by oscillating the atoms inside the cesium at the same frequency which then helps with accurate time and distance measurements. These clocks take in consideration the time dilation due to the gravitational mass as proven by Einstein’s theory of relativity.

This time correction is an integral process of the GPS as it takes in account the nanoseconds dilated due to gravity when the signal is sent from the satellites to the base station. Scientists have produced a machine called DGPS (differential global positioning system) which automatically computes the time variation and syncs it with the signal for accurate time measurements.

3-D trilateration is a complex form of the triangulation. Triangulation allows the GPS to locate a position on Earth by timing signals from three satellites by utilising the geometry of triangles and circles. Once a GPS has computed these distances of the three satellites, it begins the process of trilateration. These three satellites help pinpoint the geographical position, however with a fourth satellite it can determine the altitude of the GPS receiver which make the information more accurate.

 

[eyeseeyou]

For the following dot point I have discussed GPS. Can you see if my answer is good or not and what to add/remove from it?

• Identify data sources, gather, process and present information from secondary sources to identify areas of current research and use the available evidence to discuss some of the underlying physical principles used in one application of physics related to waves, such as:
– Global Positioning System
– CD technology
– The internet (digital process)
– DVD technology

Global Positioning System:
The GPS is made up of 24 satellites orbiting the Earth at 17,600km altitude. They are positioned in a way that the entire surface of the Earth has a line of sight between a couple of the satellites. The line of sight connection allows it to locate your position on Earth. The satellites are in conjunction to a series of ground stations which are in constantly in contact with the satellites via radio communication and manipulate the satellites movements.

The GPS are outfitted with Atomic clocks that are made up of cesium. These clocks tell precise time by oscillating the atoms inside the cesium at the same frequency which then helps with accurate time and distance measurements. These clocks take in consideration the time dilation due to the gravitational mass as proven by Einstein’s theory of relativity.

This time correction is an integral process of the GPS as it takes in account the nanoseconds dilated due to gravity when the signal is sent from the satellites to the base station. Scientists have produced a machine called DGPS (differential global positioning system) which automatically computes the time variation and syncs it with the signal for accurate time measurements.

3-D trilateration is a complex form of the triangulation. Triangulation allows the GPS to locate a position on Earth by timing signals from three satellites by utilising the geometry of triangles and circles. Once a GPS has computed these distances of the three satellites, it begins the process of trilateration. These three satellites help pinpoint the geographical position, however with a fourth satellite it can determine the altitude of the GPS receiver which make the information more accurate.

Don't you have a dotpoint word document for all this Rathin?

 

[Green Yoda]

Don't you have a dotpoint word document for all this Rathin?

huh?

 

[eyeseeyou]

huh?

Do you have a set of notes which follow all the syllabus dotpoints?

 

[Green Yoda]

Do you have a set of notes which follow all the syllabus dotpoints?

uhh andrew harvey's notes and thats bout it lol. I use the textbooks mostly

 

[Nailgun]

uhh andrew harvey's notes and thats bout it lol. I use the textbooks mostly

I reckon for HSC you should start writing your own notes (I'm not sure if you are saying you do or don't atm ahah)
That's pree typical though, there isn't much for prelim phys

 

[eyeseeyou]

uhh andrew harvey's notes and thats bout it lol. I use the textbooks mostly

Have you tried to compile a set of notes from textbooks (e.g. in2 physics, jacaranda)

 

[Green Yoda]

I am making notes lol...what I was saying was that I don't have other notes to refer to so I just use textbooks. What I've learnt is that making notes in physics is a must..whilst for biology I have wasted too much time making notes instead if remembering all the content so for the rest of yr 11 and 12 I won't make notes for bio but get a good pair and just memorise it and understand concepts via textbook.

 

[Green Yoda]

Help with 2 questions:
1. What would happen to the measured intensity of a light from a candle if the intensity at the source is doubled and the distance from the source is doubled?

2. A sound travels through a tube fitted with various pressure gauges(high and low..so basically compressions and rarefactions inside the tube). Describe the distribution of air particles if a higher frequency travels through the tube.

 

[InteGrand]

Help with 2 questions:
1. What would happen to the measured intensity of a light from a candle if the intensity at the source is doubled and the distance from the source is doubled?

2. A sound travels through a tube fitted with various pressure gauges(high and low..so basically compressions and rarefactions inside the tube). Describe the distribution of air particles if a higher frequency travels through the tube.

For 1., if we first double the power of the source, then the intensity doubles. Then if we double the distance from the source, this has the effect of 'quartering' the intensity. Since 2*(1/4) = 1/2, the end result is that the intensity is halved.