Physics marathon (hsc) (2 Viewers)

[nerdasdasd]

gather, process and present secondary information to discuss how shortcomings in available communication technology lead to an increased knowledge of the properties of materials with particular reference to the invention of the transistor

Yeah I dont have any notes on this and HSC online is useless for it.

• Problem in the early days of the radio was amplification – the received signal was extremely weak and could not produce a loud sound without being amplified
• Achieved amplification by using vacuum tubes (thermionic devices), which were very fragile, large, expensive and required high power consumption
• The invention of the transistor solved these significant shortcomings:
o Contained 3 semiconductors – NPN transistors and PNP transistors
o It was smaller, longer lasting, more reliable, less expensive and required less power
o It quickly replaced the vacuum tube in many electronic devices

 

[manscux]

That's a pretty hard question, but I haven't revised Space yet, I do that tomorrow. I'd say that the gravitational force is inversely proportional to the distance between the planets and the sun, yet we need to also consider the mass of the planets. I'd basically say that using Newtons law of Universal Gravitation we can understand that the gravitational force between planets becomes greater as the mass of the planets increase, or the distance decreases. Not sure, I'm sure someone else knows.

Could probably explain the 'motion' using r^3/t^2 = GM/4(pi^2) let the right side equal a constant. Radius proportional to time... :/

Thats actually a dot point.....

Expanding of Deswa's post .......

i would say that a satellite orbiting the earth via uniform circular motion has a centripetal force directed towards the centre of the circle to keep the satellite in motion. Newtons law of Universal Gravitation explained that it is the gravitational attraction between the earth, or another massive mass, and the satellite that acts as the centripetal force. By equating the centripetal force of an object with Newtons Law of Universal Gravitation, a better understanding in the motion of the satellite can be gained as the velocity required for the satellite to stay in orbit can be calculated.
I would show how we can do this and than say that this equation tells us that the radius is the only variable that determines the required velocity. the greater the radius of the orbit the lower the orbital velocity required.

 

[deswa1]

gather, process and present secondary information to discuss how shortcomings in available communication technology lead to an increased knowledge of the properties of materials with particular reference to the invention of the transistor

Yeah I dont have any notes on this and HSC online is useless for it.

I don't have time to write a full answer soz (hopefully someone else will) but this is the general idea:

- Early on we had stuff like radios etc. that were based on thermionic devices to amplify signals etc.. These are crap -> unreliable, big, took time to start up.
- In the 1940's, telephone networks started to expand and the unreliability become too much
- People were like 'stuff this shit' lets level up our communications
- Scientists (particularly at Bell Labs) working with semiconductors were like "fuark, this is pretty good" so they did more research into them
- The first transistor (the point contact transistor) was developed in 1948. This however wasn't that good so Willian Shockley proposed a junction transistor with an npn junction.- - Things like NPN junctions were discovered and more research was done into their properties -> essentially the transistor had been invented and was based on germanium. Germanium effs up its conducting properties when it becomes too hot and this is one of the reasons why it was later replaced by silicon
- Now BS here about why transistors go off -> they're small, fast, low heat etc. compared to thermoinic

 

[someth1ng]

Maximum EMF occurs when the flux through coil is 0 and the change in flux is a maximum. So when we draw the emf vs time graph for an ac generator do we get a cos graph?

I would not mention the bolded one because emf is only dependent on the rate of change of flux - it doesn't really matter how much flux is going through it. As for the graph, it depends on the orientation of the motor when it starts.

 

[Keelan134]

• Problem in the early days of the radio was amplification – the received signal was extremely weak and could not produce a loud sound without being amplified
• Achieved amplification by using vacuum tubes (thermionic devices), which were very fragile, large, expensive and required high power consumption
• The invention of the transistor solved these significant shortcomings:
o Contained 3 semiconductors – NPN transistors and PNP transistors
o It was smaller, longer lasting, more reliable, less expensive and required less power
o It quickly replaced the vacuum tube in many electronic devices

I don't have time to write a full answer soz (hopefully someone else will) but this is the general idea:

- Early on we had stuff like radios etc. that were based on thermionic devices to amplify signals etc.. These are crap -> unreliable, big, took time to start up.
- In the 1940's, telephone networks started to expand and the unreliability become too much
- People were like 'stuff this shit' lets level up our communications
- Scientists (particularly at Bell Labs) working with semiconductors were like "fuark, this is pretty good" so they did more research into them
- The first transistor (the point contact transistor) was developed in 1948. This however wasn't that good so Willian Shockley proposed a junction transistor with an npn junction.- - Things like NPN junctions were discovered and more research was done into their properties -> essentially the transistor had been invented and was based on germanium. Germanium effs up its conducting properties when it becomes too hot and this is one of the reasons why it was later replaced by silicon
- Now BS here about why transistors go off -> they're small, fast, low heat etc. compared to thermoinic

Cheers Lads

 

[Keelan134]

Here are some more perceptive questions.

a) A satellite was launched from Earth to Mars. What is the optimal point of interception of the satellite with mars' orbit in relation to where it was originally launched from earth to ensure minimal fuel is required for the journey? (2 marks)

b) A satellite is going to use the slingshot effect to gain maximum speed towards a distant star. At what point within the earth's orbit (see diagram) would it be optimal for the spacecraft to use the slingshot effect, and from what direction should it approach and what direction should it leave to maximise speed (assume the spacecraft can approach from anywhere) (3 marks)

View attachment 26879

a) A natural Earth 'run up' is available before launch. As the Earth rotates rapidly, a rocket posesses a large easterly tangential velocity at launch. This rotation is strongest at the equator, minimising the values of g and providing the fastest tangential velocity. The higher the altitude of the launch the less fuel needed as the distance between the craft and Earth's core is increased and with reference to Newton's Law of Universal Gravitation, this equates to a lower Gravitational force on the rocket pulling it down to Earth.

b)As Earth orbits the sun, an extra boost can be gained from Earth's orbital speed at the time of year the tangent to earth's orbit points in the desired direction. So something to do with that?

 

[barbernator]

a) A natural Earth 'run up' is available before launch. As the Earth rotates rapidly, a rocket posesses a large easterly tangential velocity at launch. This rotation is strongest at the equator, minimising the values of g and providing the fastest tangential velocity. The higher the altitude of the launch the less fuel needed as the distance between the craft and Earth's core is increased and with reference to Newton's Law of Universal Gravitation, this equates to a lower Gravitational force on the rocket pulling it down to Earth.

b)As Earth orbits the sun, an extra boost can be gained from Earth's orbital speed at the time of year the tangent to earth's orbit points in the desired direction. So something to do with that?

a) you didn't answer the question, it's only asking the best trajectory from earth to mars and where is should intercept with mars' orbit.

b) just answer the three points in the question.
- What letter would it be best to use the slingshot effect at
- What direction should it approach from
- What direction should it leave.

and I added a calculation question if you want to do that as well

 

[Keelan134]

a) you didn't answer the question, it's only asking the best trajectory from earth to mars and where is should intercept with mars' orbit.

b) just answer the three points in the question.
- What letter would it be best to use the slingshot effect at
- What direction should it approach from
- What direction should it leave.

and I added a calculation question if you want to do that as well

Eh, it wanted to know about its launch point so I just threw that at them.

OHHH now I see the diagram. S= Sun, the arrows earths orbit and the odd thing is Mars or the Star?

 

[barbernator]

Eh, it wanted to know about its launch point so I just threw that at them.

OHHH now I see the diagram. S= Sun, the arrows earths orbit and the odd thing is Mars or the Star?

question a) is different to question b) the thing on the right on the diagram is the star.

 

[Keelan134]

Should it approach from D utilise as much of the orbit as possible, leave from C into the direction of the distant star. When it says what letter best to use the slingshot effect, would it mean where to start its slingshot or where to leave?

 

[leesh95]

Calculate the amount of work that needs to be done to lift a 200 kg satellite to an altitude of 350 km?

 

[Keelan134]

Calculate the amount of work that needs to be done to lift a 200 kg satellite to an altitude of 350 km?

Delta Work = Final GPE - Initial GPE

Initial GPE = -GmM/r
=-[(6.67x10^-11 * 200 * 6.0x10^24)/(6.38x10^6)]
=-1.2545...x10^10

Final GPE
=-[(6.67x10-11*200*6.0x10^24)/(6.38x10^6 + 350000)]
=-1.1893....x10^10
GPE final - GPE initial = 556983655.3 Joules
=5.6x10^8 Joules

 

[Keelan134]

We need more info. Is the initial altitude ground level? what is the radius of the earth? what is the mass of the earth?

Mass of Earth is on data sheet, but yeah we do need radius of earth and I assumed ground level. Radius is typically 6.4x10^6

 

[LlamaBoi]

Calculate the amount of work that needs to be done to lift a 200 kg satellite to an altitude of 350 km?

Easy, W = Fd
= (200*9.8)*350000
= 6.86 x 10^8 J

Discuss Einstein's and Planck's differing views o scientific research and its place in society and politics. (4 marks)

 

[LlamaBoi]

Calculate the amount of work that needs to be done to lift a 200 kg satellite to an altitude of 350 km?

Easy, W = Fd
= (200*9.8)*350000
= 6.86 x 10^8 J

Discuss Einstein's and Planck's differing views o scientific research and its place in society and politics. (4 marks)

 

[deswa1]

Easy, W = Fd
= (200*9.8)*350000
= 6.86 x 10^8 J

Discuss Einstein's and Planck's differing views o scientific research and its place in society and politics. (4 marks)

You can't do that because you are assuming that the gravitational attraction remains constant at both heights which isn't true-> you have to calculate the different G.P.E's in order to take the weakening gravitational field into account

 

[Keelan134]

You can't do that because you are assuming that the gravitational attraction remains constant at both heights which isn't true-> you have to calculate the different G.P.E's in order to take the weakening gravitational field into account

Yeah I thought Llama's work seemed to easy to be true for Physics haha

 

[LlamaBoi]

You can't do that because you are assuming that the gravitational attraction remains constant at both heights which isn't true-> you have to calculate the different G.P.E's in order to take the weakening gravitational field into account

haha damn, I guess the complexity of the working will depend on the mark allocations but yeah you're right
btw after checking Keelan134's work, final answer should be 6.52 x 10^8 J, which is pretty close to my answer hahaha

 

[viraj30]

Question- if a stone is launched at an angle of 23.2 degrees and falls on the ground after covering 75 metres, find its initial velocity.

 

[Keelan134]

Question- if a stone is launched at an angle of 23.2 degrees and falls on the ground after covering 75 metres, find its initial velocity.

Range = v^2/g *sin2(theta)
therefore sq root of (75*9.8/ sin 46.4) = v
v=31.85 m/s