HSC Physics Question Thread

[clovvy]

Ahh no you were right! I did TORQUE, the question wanted FORCE, I didn’t read the question properly sorry!!

In return I deserve a +1 upvote as compensation for making me twist my head over this question overnight 

[Dragomistress]

Hey,
Why is 20 A and 14 D?

[Mate2425]

Hey guys would appreciate it if someone could give me a solid explanation on HSC 2014 Q17. MC

http://educationstandards.nsw.edu.au/wps/wcm/connect/d9a632e8-e0a0-439a-9869-3ce2795be292/physics-hsc-exam-2014.pdf?MOD=AJPERES&CACHEID=ROOTWORKSPACE-d9a632e8-e0a0-439a-9869-3ce2795be292-lG96GS9

Thankkkkyyyyooouu!!

[clovvy]

Hey guys would appreciate it if someone could give me a solid explanation on HSC 2014 Q17. MC

http://educationstandards.nsw.edu.au/wps/wcm/connect/d9a632e8-e0a0-439a-9869-3ce2795be292/physics-hsc-exam-2014.pdf?MOD=AJPERES&CACHEID=ROOTWORKSPACE-d9a632e8-e0a0-439a-9869-3ce2795be292-lG96GS9

Thankkkkyyyyooouu!!

Hi,
So for this question, because the alpha particle is twice that of a proton, the force applied to it within the electric field is twice as great. However, since the mass of he alpha particle is 4x that of proton, and taking into account F=ma, its acceleration is half that of the proton... Hence the correct answer should be B

[Mate2425]

Hi,
So for this question, because the alpha particle is twice that of a proton, the force applied to it within the electric field is twice as great. However, since the mass of he alpha particle is 4x that of proton, and taking into account F=ma, its acceleration is half that of the proton... Hence the correct answer should be B

Thanks Clovvy 

[Mate2425]

Hey, how do i do the process for HSC 2015 Q24C. using the elctrical energy and kinetic energy method.

Thanks,   

[clovvy]

Hey, how do i do the process for HSC 2015 Q24C. using the elctrical energy and kinetic energy method.

Thanks,   

Hi,  this is my solution
a=F/m=4×10^14/9.1×10^-11=4.4×10^16m/s/s..
Then you  use v^2=uy^2+2ay
So v=(2×4.4×10^16×0.02)^0.5=4.19×10^7m/s..

Sorry for some reason LaTeX is not working properly so I use a rough way of writing instead but hopefully that helps..

[Mate2425]

Thanks Clovvy, why do we use the projectile motion formula?
And also by any chance would you happen to know how to do the electrical energy and kinetic energy method.

[Dragomistress]

Heyyyy!
I always take quite some time in converting integers to using powers. Do you get penalised for not using powers of 10 for something like 0.00000000251? Or do you have to write 2.51x10^-9.

Can I also get some help on the attached questions?

[clovvy]

Hi, could someone explain the effect of the magnetic field on the proton (as in whether it goes clockwise or anti) and how the resultant vector points to the perpendicular direction. Thanks

hey, sorry for the delay I missed this question..

So the magnetic field will cause the proton in a circular path which moves out of the page initially, continues in an anti-clockwise direction as viewed from the right. At the same time, the electric field will cause the proton to move to the left with increasing speed. So the resultant motion will be basically be the sum of the vectors based on the direction of the motion of proton, which will look like its stretched towards the left. Also the radius shown will be decreasing as the proton loses energy as it radiates electromagnetic radiation as it is an accelerating charge.

[clovvy]

Thanks Clovvy, why do we use the projectile motion formula?
And also by any chance would you happen to know how to do the electrical energy and kinetic energy method.

hey sorry I didn't respond quick enough... It is asking for velocity and this is probably the best way to do it imo.., because the initial velocity (hence the KE) of the electron on the cathode is considered to be effectively zero. The acceleration of an electron within a uniform field can easily be found with F=ma since you know the force and the mass (force calculated from part ii assuming you've done it).. with regard to using projectile, it works because the only force acting on the electron is the electric field as it moves (similar to the behaviour of projectiles)- although I am hoping that someone can explain that better than myself...

and I don't know how to use electrical/kinetic energy method sorry.., if Jamon or someone expert could lend a hand that would be a great help for me too

[clovvy]

Heyyyy!
I always take quite some time in converting integers to using powers. Do you get penalised for not using powers of 10 for something like 0.00000000251? Or do you have to write 2.51x10^-9.

Can I also get some help on the attached questions?

hey man,
So for the Michelson and Morley question, I remember that one as I did do the ruse trials and tbh  it is confusing, like I am 100% certain the the aether is not a solid so I do pick D when I first did it online..., still doesn't make sense to me imo so I need someone to be able to explain that to me.. I also suspect that the answer provided is a typo..
So for the motors question...
This is more like an elimination of wrong answers... eliminate A as it is obviously wrong so eliminate that... and given where A and B is, both the force and the torque will be at maximum. therefore both F and the torque will reverse direction after rotating 90 degrees... so we would expect sudden change in force so D is eliminated...  obviously the torque will not be at stationary hence the most correct should be B (hope my explanation make sense)..
For the last one, just plug in sin30 because it enters the magnetic field at an angle of 30, and using the rhsr, the force should go into page...

I hope I have helped you a bit..

[clovvy]

Hey,
Why is 20 A and 14 D?

For Q14, as side Y enters the magnetic field a voltage will be induced. As X enters it will also produce an equal voltage, as it is moving through the field in the same direction. This leads to NO difference in voltage between X and Y while they are both within the field. As they leave the field on the other side, the voltage is again induced but in opposite direction to the original voltage when it enters the field. So out of the 4 option, only A shows this..
For Q20, if the gravitational force weakens, the period it took to complete one whole orbit will reduce, which eliminates option A and B straight away.. To pick between 0.28 or 0.5, I am not sure how to do it either so I will need help with that if anyone is kind enough to help...

[Mate2425]

Hey Jamon,
For HSC 2011 Q21a, i am strugling to understand why they didn't connect line of best fit from point of (T=12) and (T=36) and also how do they know precisely where to position the line between the array of points provided. I followed my method and determined a resistance of 0.1265 ohms which was out by 0.0002 ohms would they penalise this answer and the graph or one or the other?

Many Thanks! 😁

[clovvy]

Hey Jamon,
For HSC 2011 Q21a, i am strugling to understand why they didn't connect line of best fit from point of (T=12) and (T=36) and also how do they know precisely where to position the line between the array of points provided. I followed my method and determined a resistance of 0.1265 ohms which was out by 0.0002 ohms would they penalise this answer and the graph or one or the other?

Many Thanks! 😁

Hey man,
For these type of question, you are looking at trends shown with the given values and you try to make an estimate... In this case, the relationship looks linear and you want to 'average out' your results which is why the line is drawn 'near' it but did not cross it as it is a 'line of best fit'...
I hope that make sense.... regarding the value of resistance at 24 degrees, your answer is close enough so I don't think they will penalise you too much I am sure range between 0.1265-127 is acceptable...

hey man,
So for the Michelson and Morley question, I remember that one as I did do the ruse trials and tbh  it is confusing, like I am 100% certain the the aether is not a solid so I do pick D when I first did it online..., still doesn't make sense to me imo so I need someone to be able to explain that to me.. I also suspect that the answer provided is a typo..
So for the motors question...
This is more like an elimination of wrong answers... eliminate A as it is obviously wrong so eliminate that... and given where A and B is, both the force and the torque will be at maximum. therefore both F and the torque will reverse direction after rotating 90 degrees... so we would expect sudden change in force so D is eliminated...  obviously the torque will not be at stationary hence the most correct should be B (hope my explanation make sense)..
For the last one, just plug in sin30 because it enters the magnetic field at an angle of 30, and using the rhsr, the force should go into page...

I hope I have helped you a bit..

Getting back to the Michelson and Morley question, the correct answer is indeed D so I was correct... The solution provided for Q7 was a typo so the answer is wrong because the aether is not a solid (I was positive I was correct, and I double checked with a ruse physics teacher which I knew in person)...