Stopsign's Physics Marathon (1 Viewer)

[Stopsign]

HSC/2006 Physics Marathon

Hey physicists!

Welcome to my physics marathon thread. This marathon enables your minds on physics to keep on running.
You know the drill so let's start.

First Question:
Describe Newton's Analysis of Escape Velocity.

(Reactivated on Thursday, 10th August 2006)

 

[felixcthecat]

ummm.... y does it hav to start off so hard??

Newton envisaged a cannonball launched horizontally on top of a high mountain at a location where air resistance is negligible... he said that the cannon ball would start travelling horizontally, but its path would immediately begin to bend downwards.WIth too little velocity the cannon ball would fall bac to earth.. at too great a velocity, the cannon ball would um... u kno wut i mean!.. and at the 'right' velocity, an object could be made to orbit around a planet

haha.. was i right??

here's an easy one ^^".. define centripetal force and state its equation!

 

[Stopsign]

Centripial force
A centre-seeking force of an object which allows it to maintain its circular motion. It's given by F=mv^2/r.

Next Question:
Describe the safety issues that must be considered when a space craft is re-entering the earth's atmosphere.

 

[acullen]

The re-entry angle must be very precise, too shallow and the craft will effectively "bounce off" the atmosphere, too steep and you have one barbequed space craft. Any critical strutures (particularly in the wing assuming we are talking about a re-usable craft) should be well thermally insulated against the superheated plasma gas that forms around the spacecraft on re-entry. Due to the ionised gas formed around the craft, radio contact with the ground is lost for an amount of time on re-entry, the craft must be able to navigate during this time solely using it's own gyroscopic instruments (i.e. this means secondary and backup inertial navigation instruments are required).

Describe the caloric theory of heat.

 

[Stopsign]

I had to reactivate this marathon to keep ourselves studying.


Outline how JJ Thomson calculated the mass to charge ration of electrons.

 

[JhK89]

pfft JJ thomson o well...

JJ thomson incorporated charged plates inside the CRT. Thomson was able to verify the hypothesis suggested by Crookes. That CR will be deflected by electric fields. By passing cathode rays betwen parallel plates connected to a power source Thomson observed that the rays moved towards the positive part of the plates showing that the rays were negatively charged.

i think thats right...

heres the next question..

Define the Motor Effect

 

[rawker]

Charged particles moving in an external magnetic field experience a force. If the charged particles are confined to and flowing through a conductor that is an external magnetic field, the conductor will also experience a force.

Describe the term "orbital decay".

 

[sinist4]

"orbital decay" is wen a satellite is in low earth orbit and experiences friction, which is called atmoshperic drag. this occurs wen it moves through a very thin atmosphere, this causes the satellite to slow down and lose aititude.


Next Q: outline the nature of "inertial frames of refence".

 

[Forbidden.]

I'm not up to the HSC course ..

Try ..

A truck of mass 4x10³ moving at 3.5ms^-1 collides with a stationary truck to which it becomes automatically coupled. Immediately after the impact the trucks move along together at 2ms^-1. Find the mass of the second truck.

 

[sasquatch]

I'm not up to the HSC course ..

Try ..

A truck of mass 4x103 moving at 3.5ms-1 collides with a stationary truck to which it becomes automatically coupled. Immediately after the impact the trucks move along together at 2ms-1. Find the mass of the second truck.

You cant forget about this...they wouldnt ask a question like this in the hsc..

momentum before = momentum after
(4x10^3)(3.5) + (0)(m) = (4x10^3 + m)(2)
m = 3000 kg

 

[sinist4]

from b4 Next Q: outline the nature of "inertial frames of refence".

 

[Forbidden.]

You cant forget about this...they wouldnt ask a question like this in the hsc..

momentum before = momentum after
(4x10^3)(3.5) + (0)(m) = (4x10^3 + m)(2)
m = 3000 kg

I'm afraid that was wrong

Spoiler

Only joking, your final answer was correct ...

 

[passion89]

from b4 Next Q: outline the nature of "inertial frames of refence".

An inertial reference frame is one in which an object is either moving at constant velocity, is at rest or (to sum it up) is not accelerating/deccelerating in any way.

In an inertial frame of reference, there is nothing you can use to tell you whether you are moving or not.

All inertial reference frames are equivalent when applying Newton's laws.




Next question:
Outline Hertz's experiments in measuring the speed of radio waves and how they relate to light waves.

 

[angmor]

ITS TIME to revive this thread. im going to answer
Outline Hertz's experiments in measuring the speed of radio waves and how they relate to light waves.




Hertz set up his experiment so that a transmitter would produce rapidly oscillating sparks. a receiver made of a half loop of wire would have induced sparks, showing that waves had been transversed across from the transmitter to the receiver.
by measuring the wavelength of the waves bouncing of the receiver against a detector, and as he already knew the frequency of the oscillating sparks in his transmitter, he was able to use the universal wave equation v=fλ to calculate the speed of the radio waves.
in doing this, he showed that the speed of radio waves was also similiar to that of light waves. this gave evidence that both radio waves and light waves were somehow related, leading them to believe that both radio and light waves belong the the Electromagnetic wave spectrum.


next : explain why, when the current of a motor measured at full speed is less than when it is forcibly stopped to rotate.

 

[bboyelement]

when its stopped, no change in magnetic flux hence no induced back emf in the motor according to Faraday's law of induction. the current of opperation is the current supplied minus the back emf ... when there is no back emf the current of operation will be really high... which opposes to when a motor is running at constant speed where the back emf and the operating current is equal.

explain the michelson and morley experiment and how einstein's posulates were able to explain the result.

 

[sinist4]

^ dam thats a long one..., i hate these long ones. i'll leave it for a pro to do lol

 

[angmor]

lol yeah....lets keep it short and simple. no essay like 8 mark questions please.

 

[Ioup]

Briefly explain the difference between an AC Synchronous motor and an AC induction motor.