Multiple Choice (4 Viewers)

[cyko]

Q5 .. why is there so much debate .. its C

just consider the full time of flight which is

t = 2Vsin@/g

and the max range

x = (V^2)sin2@/g

 

[Mellybum]

http://galileo.phys.virginia.edu/classes/109N/more_stuff/Applets/ProjectileMotion/jarapplet.html

check this out

sucked in C

Hm... well there u go...

 

[dipis]

Think about Newton's concept of escape velocity. When the cannon is fired slower, it curves into the earth. So when this rocket goes slower, what do you think its going to do?

but thats when something starts on earth and crashes into the earth, its different when its in orbit. Low earth orbitters need to travel heaps faster than geo stat to match their falling motion with the curve of the earth, uthawise they will crash into the earth

 

[Dumsum]

but thats when something starts on earth and crashes into the earth, its different when its in orbit. Low earth orbitters need to travel heaps faster than geo stat to match their falling motion with the curve of the earth, uthawise they will crash into the earth

Where did the gravitional potential energy to get it out to a larger orbit come from?

 

[dipis]

Where did the gravitional potential energy to get it out to a larger orbit come from?

From the rocket that was fired, same as any other rocket leaving earth.

 

[~Hyperion~]

A cannot be the answer. The formula v = rt(Gm/r) only applies for orbital velocity. When the probe's speed is halved, it is no longer an orbital velocity hence using that formula to deduce an increase in radius is invalid. Whether the answer is C or D, I can't say for sure.

 

[thunderdax]

but thats when something starts on earth and crashes into the earth, its different when its in orbit. Low earth orbitters need to travel heaps faster than geo stat to match their falling motion with the curve of the earth, uthawise they will crash into the earth

OK, here's an analogy for you. A car is turning in a circular path. It increases its speed but its force towards the center of the circle stays the same. It hence underturns and skids off the road. Consider this satellite as a car turning in a circle. When the car loses speed but force stays the same it overturns, moving inwards from the road (the orbit).

 

[thunderdax]

A cannot be the answer. The formula v = rt(Gm/r) only applies for orbital velocity. When the probe's speed is halved, it is no longer an orbital velocity hence using that formula to deduce an increase in radius is invalid. Whether the answer is C or D, I can't say for sure.

Actually, I agree with this. There seems to be no way to tell which one of these it would be.

 

[SlaminSammy]

Mellybum... dont listen to what those "Geniuses" have to say... They are wrong. Time of flight is dependant only upon the vertical component of the projectiles motion.... keeping it simple... is xsin40 greater or less than xsin50... x sin 50 is greater... hence it has a higher max height and a greater time of flight....

Projectiles fired at 45* to the horizontal have a max range! Projectiles fired at complementry angles ie 40 and 50 have the same range! didnt you learn that this year... yeeesh.... Children these days...

NOTE q 4 = D
not many people got this right... if you lose kinetic energy you must lose gravitational potential energy... sooooo no one studies orbital decay... its kinetic energy is lost to heat... as it decreases in kinetic energy it must also decrease in gravitational potential energy... hence it will drop down into a lower orbit... but then it will speed up, because at lower altitudes it must have a higher velocity to maintain its orbital motion... and it will experience more drag... greater loss of kinetic energy... hence drop down further.. this will continue until the satilite's orbit completely decays and it smashes into earth.

only a dingus will say A... if we lose kinetic energy how can it enter an eliptical orbit or escape the earths gravitational field... again no one studies.. remember newtons concept of escape velocity... You need to suply the satalite with kinetic energy in order to escape the earths gravitational feild... so think of that...


just so you know 7 was D... in A... if we use the right hand grip rule and we know that the force applied to the coil is in an anticlockwise direction... we can see that in A... a feild of stength developes on the left hand side of the coil and a feild of weakness is developed on the inside of that wire.. then we can tell by the motor effect that the force would be in a clockwise direction... hence the law of conservation of energy would be violated... we should know... unless were shmucks... that B and C is definately wrong... and physically impossible.. note to smartasses: the arrow indicates the net current flowing through the coil... not one for conventional current and one for induced back current... Hence the answer is D.. and by using the right hand grip rule.. we can see that the force created by the motor effect, of the interaction of the external magnetic feild and the magnetic feild of the induced current acts against the motion of the coil... ie in an anticlockwise direction.

Everyone seems to get the concept with 8 incorrect.... A changing magnetic flux will induce a current in the secondary coil... regardless if the current is direct or alternating.. as the switch is closed current flows through the primary coil for the first time and hence a changing magnetic flux exists... however once the current reaches it maximum the magnetic flux threading the secondary coil will be constant.. hence if you can guess correctly NOW that you understand the answer is C...

q 9 is about eddy currents. eddy currents will be produced in a conductor is it is passing through a changing magnetic field... i cant believe that someone would refute this... your stuborn if you do... ITS A CONDUCTOR... IT HAS FREE ELECTRON... and if considered relativistically.. the electrons are moving in a magnetic field and hence experience a force which by lenzs law with oppose the motion which caused them! so the 2 copper rings travel slower than the plastic ring... However, the copper ring with a slit... will have smaller eddy current induced hence it will not slow down as much as ring Q... hence the answer is B...

 

[Mellonie]

12 is not A liek eevyone keeps saying...

plank couldnt explain what he had found, einstein instead explained it.

HAlf the multiple answers everyone putting up is wrong, and does not make sense!!!! N i dont want to put mine up cuz its prolly equally wrong, but can someone put somethnig up which is coreect like form teachers. And y is ppl putting multiple choice answers up syaing this isdefinately correct making their selves look so stupid.

 

[rama_v]

To all those wanting an explnation for the projectile question, the two formulas u need are
range = V²Sin2@/g and Max Height attained Height = V²Sin²@/2g

Just say that V = 1 and g = 1 for convenience

Sub in 40 degrees and 50 degrees respectively. you will find that the canon shot at 50 degreees attains a higher maximum height, but the same range as the canon shot at 40 degrees. Hence because height is higher, then the time of flight is longer.

 

[thunderdax]

just so you know 7 was D... in A... if we use the right hand grip rule and we know that the force applied to the coil is in an anticlockwise direction... we can see that in A... a feild of stength developes on the left hand side of the coil and a feild of weakness is developed on the inside of that wire.. then we can tell by the motor effect that the force would be in a clockwise direction... hence the law of conservation of energy would be violated... we should know... unless were shmucks... that B and C is definately wrong... and physically impossible.. note to smartasses: the arrow indicates the net current flowing through the coil... not one for conventional current and one for induced back current... Hence the answer is D.. and by using the right hand grip rule.. we can see that the force created by the motor effect, of the interaction of the external magnetic feild and the magnetic feild of the induced current acts against the motion of the coil... ie in an anticlockwise direction.

...

q 9 is about eddy currents. eddy currents will be produced in a conductor is it is passing through a changing magnetic field... i cant believe that someone would refute this... your stuborn if you do... ITS A CONDUCTOR... IT HAS FREE ELECTRON... and if considered relativistically.. the electrons are moving in a magnetic field and hence experience a force which by lenzs law with oppose the motion which caused them! so the 2 copper rings travel slower than the plastic ring... However, the copper ring with a slit... will have smaller eddy current induced hence it will not slow down as much as ring Q... hence the answer is B...

Lol, who's the genius Slaminsammy? Just so you know 7 is A, this is about electromagnetic induction. By Lenz's law the induced current must OPPOSE the motion and hence move the opposite way. Hence the force must be anticlockwise and the answer is A.

Q9: Eddy currents are circular currents flowing in a piece of metal. How can they be circular if the ring isn't complete? Hence ther are no eddy currents in R and the answer is C.

Q12: Einstein didn't explain blackbody radiation. He explained the photoelectric effect. Planck explained that light is quantised and proved the relationship E=hf.

 

[HSCExamMarker]

1. C is wrong because you are thinking about vertical velocity being 0 however at the top there is still horisontal velocity
if you did 3unit maths this would be a very easy concept to understand.
and ofcourse the velocity is always changing so its A.

8. battaries only work on DC current... have you ever seen a AC battary? It doesn't even make sense..

anyways u picked D which is again definatly wrong (because the graph u are thinking of is VOLTAGE VS TIME not CURRENT VS TIME) and B and C cannot be corret because we were not given enough information about the resistor (even though it wasnt even needed if u knew battaries are DC)

9. it could be B but definatly not A... Q will NEVER fall before R

1. you are correct
8. nope there is still changing magnetic flux since u push the switch. hence (c)
it will hav current induced for a short time then 0 no magnetic flux

9. def B
copper induces the current flowing opposite direction hence slower.

 

[Rekkusu]

Lol, who's the genius Slaminsammy? Just so you know 7 is A, this is about electromagnetic induction. By Lenz's law the induced current must OPPOSE the motion and hence move the opposite way. Hence the force must be anticlockwise and the answer is A.

Q9: Eddy currents are circular currents flowing in a piece of metal. How can they be circular if the ring isn't complete? Hence ther are no eddy currents in R and the answer is C.

Q12: Einstein didn't explain blackbody radiation. He explained the photoelectric effect. Planck explained that light is quantised and proved the relationship E=hf.

Actually Thunderdax I agree with your answers as well!

Photoelectric effect and the explanation of 'photons' was by Einstein, but it was Planck who actually discovered the relationship between wavelength and energy released/intensity.

Eddy Currents are indeed only formed when a metal is fully connected, so in other words a complete ring can only have eddy currents forming.

 

[cziLofty]

ok for Q12 this is coming straigh from the textbook HSC Success One HSC which i had happened to read last night. Ironically it was also Q12)
12) Early obervations, and experiments, on the photoelectric effect produced results which seemed difficult to explain with exsisting theories. Which of the following was the first to provide a real explanation of the results observed in experiments on the photoelectric effect?
(A) de Broglie
(B) Hertz
(C) Einstein
(D) Planck
Answer: It was Einstein, in 1905, using the concept of the photon, and quantised energy, who first provided a successful explanation for the results collected in experiments involving the photoelectric effect.
So for our questions 12 the answer was clearly B Einstein

Also for Q9 say u had a peice of wire and turned it into a loop so that the ends werent touching...put a magnet in it and nothing happens. Tie the wire together and put the magnet through. You will feel a force caused by the eddy currents as the circuit is complete, so the answer is C

 

[§joe§]

I thought the multiple choice was s***, i dont think i went that bad but the questions were really crap

 

[Mellonie]

ok for Q12 this is coming straigh from the textbook HSC Success One HSC which i had happened to read last night. Ironically it was also Q12)
12) Early obervations, and experiments, on the photoelectric effect produced results which seemed difficult to explain with exsisting theories. Which of the following was the first to provide a real explanation of the results observed in experiments on the photoelectric effect?
(A) de Broglie
(B) Hertz
(C) Einstein
(D) Planck
Answer: It was Einstein, in 1905, using the concept of the photon, and quantised energy, who first provided a successful explanation for the results collected in experiments involving the photoelectric effect.
So for our questions 12 the answer was clearly B Einstein

Also for Q9 say u had a peice of wire and turned it into a loop so that the ends werent touching...put a magnet in it and nothing happens. Tie the wire together and put the magnet through. You will feel a force caused by the eddy currents as the circuit is complete, so the answer is C

OFcourse !2 is B I AGREE, Y THE HELL CANT PPLA CCEPTSOEMTHING SO SIMPLe. GOd anyway lets like try n get real answers rather then agruing some obvious ones

 

[KFunk]

I went for:

1. A
2. D
3. B
4. D (dunno, kind of looked like what would happen )

5. C (sin@ = sin(180-@) and range is based on sin2@ so range doesn't change. Increasing the angle means that there is a larger vertical component of the velocity increasing time of flight)

6. B (random question? The woman has a chessy smile, so it must be B)

7. D (It's at the cusp where current changes direction but (using the motor effect stuff) I'm pretty sure it's starting to go in the direction where induced current is anti-clockwise)

8. C (Initially I put A 'cause it's DC but of course you get that initial kick when the current kicks in which creates a temporary change in flux. C was the only one with a brief current reducing to zero so I went with it)

9. C (eddy currents can still for in R *but* in order to appose the magnet the eddy currents would have to go around the ring - which can't happen in R)

10. B (I wasn't sure whether it was B or C. I figured the closest part of the wire's magnetic field would be the vertical travelling part hence you would want to avoid horizontal slabs/eddy currents though I'm not certain)

11. B (... I think )
12. A (Planck explained that shit)
13. C (well... you wouldn't *see* a hole 'level' would you?)
14. B
15. C (They would experience a force via motor effect... still a bit different)

 

[mrkotter]

ok for Q12 this is coming straigh from the textbook HSC Success One HSC which i had happened to read last night. Ironically it was also Q12)
12) Early obervations, and experiments, on the photoelectric effect produced results which seemed difficult to explain with exsisting theories. Which of the following was the first to provide a real explanation of the results observed in experiments on the photoelectric effect?
(A) de Broglie
(B) Hertz
(C) Einstein
(D) Planck
Answer: It was Einstein, in 1905, using the concept of the photon, and quantised energy, who first provided a successful explanation for the results collected in experiments involving the photoelectric effect.
So for our questions 12 the answer was clearly B Einstein

The question is about black body radiation so this question has nothing to do with it. Obviously Planck is the answer

 

[mrkotter]

I went for:


10. B (I wasn't sure whether it was B or C. I figured the closest part of the wire's magnetic field would be the vertical travelling part hence you would want to avoid horizontal slabs/eddy currents though I'm not certain)

Use the right hand grip rule to find the direction of magnetic field. In B the currents and still travel so the answer is C