HSC Physics Question Thread

[jamonwindeyer]

I tried subbing the values into .5mv^2 but nothing worked out

Hey! You'll need to calculate the relativistic mass of the proton using the mass dilation formula:



You know the mass of the proton and its speed, which gives you \(m_v\). This is the mass you use to calculate the kinetic energy, and then you compare that with the kinetic energies of the other objects. You could calculate their relativistic masses as well, but the effects of their velocity are negligible

Completely lost as to this question - thought the answer was C but apparently it's D - why?

A photon doesn't have mass so that formula wouldn't work! D makes sense, we can find the energy of proton using its rest mass (which is a known quantity)

Reminder: Try to use the 'Modify' button to add questions to your previous post rather than double posting twice in a row!

[naezeroth]

@sidzeman

Photons are massless particles and thus the formula E = mc^2 does not really apply to it. Photon energy is described by Planck's relationship E = hf where h is Planck's constant. Thus by logical deduction as it is not A/B/C it must be D

[sidzeman]

ahhhh okay that makes sense cheers

[winstondarmawan]

Hey! Would appreciate help with this question. The answer is A, apparently.
https://scontent-syd2-1.xx.fbcdn.net/v/t35.0-12/20747559_1529460377113486_1121039749_o.png?oh=2c0146af143515c0630bd04c5205e36f&oe=598E016E

[blasonduo]

Hey! Would appreciate help with this question. The answer is A, apparently.
https://scontent-syd2-1.xx.fbcdn.net/v/t35.0-12/20747559_1529460377113486_1121039749_o.png?oh=2c0146af143515c0630bd04c5205e36f&oe=598E016E

Hello! This is testing your knowledge on both Lenz's law and electromagnets.

When a south pole is moved towards a solenoid, to obey Lenz's law and the law of conservation of energy, it must oppose this change, and thus a south pole will be created.

Now we need to know in which direction the current will have to flow to make the left side of the solenoid a South pole. If the current is going CLOCKWISE, then a south pole will be produced. So from this, follow where the current flows where it must be going CLOCKWISE and you'll see it'll go through X first, to Y. So it HAS to be A OR B.

For point P, we must know how magnetic field lines must flow in an electromagnet, which is from SOUTH to NORTH. With this the force is going left to right, and thus point P will experience a force to the right so it is A!

Hope this helps!

[aaronster]

Could you please explain the concept of ratios in Space questions and the example below as well Pls

[Shadowxo]

Could you please explain the concept of ratios in Space questions and the example below as well Pls

For that question:
You should remember
This means the gravitational force will be the same on both objects - Newton's third law also says "Each action has an equal and opposite reaction" which confirms this. The gravitational force on object X from Y = gravitational force on object Y from X. But, the acceleration on each will be different due to their different masses.
Note: This applies to us and the earth too. The gravitational force on us from the earth is the same as the gravitational force the earth experiences from us! But, the earth's mass is far far greater than ours so it hardly moves while we feel it quite a bit.

Ratios in space questions: could you elaborate please?
If something is in orbit, Then the gravitational force is the centripetal force so Fg = Fc

[jamonwindeyer]

Could you please explain the concept of ratios in Space questions and the example below as well Pls

Hey! So as said above, the example you've provided is a trick. The force on each object is the same, the ratio is 1:1!

When you are asked to find a ratio of Quantity 1 to Quantity 2, that means dividing them:



So if for example looking at forces, \(Q_1=F\) but \(Q_2=2F\), then the ratio \(Q_1:Q_2\) would be 2:1

Often the expressions are more complex, not just \(F\), but that's the idea!

[aaronster]

thanks for the help

[itssona]

heeey how do i do this using inverse square law (thank you
light froma torch 200km away is 20 units. How bright is it 120 km away?

[AlphaGeek]

Could anyone please help me by explaining the differences in graphs of Torque, Emf, Current, Voltage for AC & DC Motors/Generators. I keep seeing so many variations online when I search for them. Thank you.

[blasonduo]

heeey how do i do this using inverse square law (thank you
light froma torch 200km away is 20 units. How bright is it 120 km away?

[jamonwindeyer]

Could anyone please help me by explaining the differences in graphs of Torque, Emf, Current, Voltage for AC & DC Motors/Generators. I keep seeing so many variations online when I search for them. Thank you.

Hey! So these graphs are representations of some pretty important concepts - Electromagnetic induction, back EMF, Lenz's Law, etc etc. To understand the graphs you need to understand those concepts, there's no set pattern unfortunately! I've written some nice succinct guides on Motors and Generators, they are linked in the middle of this resource list. Perhaps they would be helpful?

If there are any specific examples of graph questions you are confused about, upload em! Happy to help

[Sukakadonkadonk]

Hi, how would this be done?

Thanks.

[jamonwindeyer]

Hi, how would this be done?

Thanks.

Hey! So we use the centripetal force formula:



We have mass and we have radius (half the diameter, 0.25 metres) - We just need velocity! We know it completes 10 revolutions in 65.2 seconds, so we use that to calculate velocity:



Once you've got that, sub into your original formula for the answer!! Doing this I get:



Hmm. That's odd - Anyone see what I've done wrong here? Maybe we need to compensate for gravity with an upwards force as well to keep the circle horizontal but that seems a bit odd for how they've worded it

Surely it's not A, technically it is the closest but come on...