HSC Physics Question Thread

[Alexicology]

Oh definitely not a correction, your reasoning is correct too! Like, from the point of view of the coil it might as well be AC just tricky questions being tricky

Oh ok

[Shafidontcry]

What do you guys think?

[jakesilove]

What do you guys think?

Hey! I would suspect that the graph has to be continuous; the conductor will speed up, slow down and stop with continuous movement, and thus the change is voltage would have to be continuous. Thus, I suspect it is C?

[jamonwindeyer]

What do you guys think?

Remember that the size of your induced EMF (voltage) is proportional to the RATE OF CHANGE of magnetic field. So, the size of your voltage is proportional to the speed at which that conductor is moved through the field.

We don't know whether the movement is at a constant speed or if there is acceleration, but we do know that there is movement to the left, then the right, then the left. So we should expect a positive voltage (based on the graphs), then a negative voltage, then a positive one again.

That rules out B and C. A doesn't seem right to me either, because it has a constant acceleration in the positive direction besides a quick sudden change in the negative direction in the middle there. Like, A would imply the rod accelerates to the left at a constant rate, then immediately starts moving in the opposite direction instantaneously, slowing down and stopping, then accelerating back left. It just doesn't seem sensible, though I think it might be possible.

I'm going with D. It shows periods of sustained speed and acceleration, which makes more sense for the scenario at hand!

Edit: Welcome to the forums btw!

[Bubbly_bluey]

Hi guys! i honestly don't know where to start in this question 
Thank you 

[dux99.95]

Hey
My question is, if you had to quickly study for SPACE  and Motors & generators, how would you do it?
Like, whats most important in each e.g focus on pracs more in SPACE, focus on calculations more in Motors & generators (these are just examples, idk if you should actually do that).
Obviously I should study EVERYTHING but half yearlies are soon - so what should I do?

[jamonwindeyer]

Hi guys! i honestly don't know where to start in this question 
Thank you 

Hey Bubbly!

So for this one, we need to know the right hand grip rule for finding the direction of magnetic field around a current carrying wire. It's not hard, just give yourself a thumbs up with your right hand. If the thumb points in the direction of current, your fingers wrap around the wire in the direction of the magnetic field!

If you apply this analysis to this question, you'll find that two wires cause a field into the page, and one causes a field out of the page. So the strength of the field in the middle will be \(B\) - The strength of the field from a single wire, because the other two cancel out the direction, by the same logic, will be into the page - The answer is A

[jamonwindeyer]

Hey
My question is, if you had to quickly study for SPACE  and Motors & generators, how would you do it?
Like, whats most important in each e.g focus on pracs more in SPACE, focus on calculations more in Motors & generators (these are just examples, idk if you should actually do that).
Obviously I should study EVERYTHING but half yearlies are soon - so what should I do?

Hey Saloni! If I had to prioritise my content, it would be being able to explain stuff. So, being able to see a dot point and go, "Yep, I can explain Back EMF/Time Dilation/Conditions of Reentry/etc etc." You need to understand your content. The calculations aren't as important to practice (if you must choose) because you get your formula sheet, and that is half the battle. The practicals are important, but ultimately won't be worth as many marks as understanding the theory behind your syllabus dot points!

So I'd be dot pointing the more explanatory dot points and focusing on those, or even just brainstorming around the syllabus dot points to see which ones you know and which you don't! Then, just study your notes and do practice questions to get back on track

I hope that helps! Be sure to come to us if you have any questions about the content before your exam, best of luck!

[dux99.95]

Yep that definitely helped! Other question (not physics related tho), how do I see the direct reply to my question? I click on the notification thingo and it leads me to this entire post. Then I have to click on the last page and sift to find my answer - Is it supposed to be like that?

[jamonwindeyer]

Yep that definitely helped! Other question (not physics related tho), how do I see the direct reply to my question? I click on the notification thingo and it leads me to this entire post. Then I have to click on the last page and sift to find my answer - Is it supposed to be like that?

Sure! When you view the notification (I don't use them myself so memory is fuzzy), you should see page numbers below the thread title? If so, you can just click the most recent page and your response will almost always be there!!

Right now there is no way to jump straight to the person who quoted you - Trust me, that's something on my wish list!

[Bubbly_bluey]

Hey guys! I find this question get asked a lot in exams but i still can't get my head around the concept of momentum during rocket launches. I know that it is conserved by newton's third law but my question is: does the momentum for the rocket and gas change during different stages of the launch? and if so how does it change? (please dumb down the explain wherever you can )

[kiwiberry]

Hey! I'm having trouble understanding this question:

A compass placed on a table points north. In which direction should a conductor, placed directly above the compass, carry current in order to reverse the direction of the compass needle?

Thanks

[jamonwindeyer]

Hey guys! I find this question get asked a lot in exams but i still can't get my head around the concept of momentum during rocket launches. I know that it is conserved by newton's third law but my question is: does the momentum for the rocket and gas change during different stages of the launch? and if so how does it change? (please dumb down the explain wherever you can )

Hey Bubbly!

So basically, the total momentum of the rocket and fuel system is constant (and remains equal). The momentum of the rocket itself changes, as does the change in the momentum of the fuel, but they will always exactly cancel each other out!

The explanation of exactly what happens to a rockets velocity and mass (and thus momentum) throughout launch is something I've covered here - Give it a read a few times and hopefully it makes sense! Otherwise definitely send any follow up questions my way!

[jamonwindeyer]

Hey! I'm having trouble understanding this question:

A compass placed on a table points north. In which direction should a conductor, placed directly above the compass, carry current in order to reverse the direction of the compass needle?

Thanks

Hey Kiwi!

So we need to use the right hand grip rule here, but backwards. We need a magnetic field running south (compasses align with magnetic field lines). So, we need a magnetic field running down the compass. Hold up your right hand in a thumbs up, then align your fingers to point downwards on your imaginary compass. That should have your thumb pointing to the left. So, we need a current flowing to the left (WEST), assuming we have a conductor above the compass running from East to West

Aha, this is hard to explain with text, does this make sense kiwi?

[kiwiberry]

Hey Kiwi!

So we need to use the right hand grip rule here, but backwards. We need a magnetic field running south (compasses align with magnetic field lines). So, we need a magnetic field running down the compass. Hold up your right hand in a thumbs up, then align your fingers to point downwards on your imaginary compass. That should have your thumb pointing to the left. So, we need a current flowing to the left (WEST), assuming we have a conductor above the compass running from East to West

Aha, this is hard to explain with text, does this make sense kiwi?

Yes that does!! Thanks Jamon