HSC Physics Question Thread

[katnisschung]

A mass carrier is attached by a length of fishing line to another mass carrier
The line passing through a tube which is moved in such a way as to keep the first mass carrier moving in a circle
Hypothetically if the centripetal force was greater than the weight force would the pass go flying outwards?

[jamonwindeyer]

A mass carrier is attached by a length of fishing line to another mass carrier
The line passing through a tube which is moved in such a way as to keep the first mass carrier moving in a circle
Hypothetically if the centripetal force was greater than the weight force would the pass go flying outwards?

Hey Katniss! I'm having a bit of trouble picturing this scenario, is it something from a book? Do you think you could attach a diagram or maybe even draw one to help me understand it a little better?

[katnisschung]

Hey Katniss! I'm having a bit of trouble picturing this scenario, is it something from a book? Do you think you could attach a diagram or maybe even draw one to help me understand it a little better?

[jamonwindeyer]

ATTACHMENT

Awesome! Okay, I'm with you now. So the weight force of the larger mass carrier is providing the centripetal force that keeps the smaller mass carrier in uniform circular motion.

Your interpretation (as I interpret it) is 100% spot on. If the mass carrier is in motion with a radius and velocity such that the force required to maintain it is greater than the weight force, then yes, it will fly outwards. Or perhaps just slowly wobble into a wider circle to re-establish the balance? We can't tell which, but yes, the moving mass will definitely move outwards if the weight force isn't sufficient to maintain the motion

[katnisschung]

for my first hsc assessment we have a physics prac
and the notification gave very limited info regarding what we will be tested on
(it only said the unit of "space")
its worth 25% which is quite a bit, however this is only my second practical test in science.

advice on how to study and does anyone have any practice papers for pracs so i could possibly
carry it out at home? my intuition tells me it could have something to do with projectile motion

[jakesilove]

for my first hsc assessment we have a physics prac
and the notification gave very limited info regarding what we will be tested on
(it only said the unit of "space")
its worth 25% which is quite a bit, however this is only my second practical test in science.

advice on how to study and does anyone have any practice papers for pracs so i could possibly
carry it out at home? my intuition tells me it could have something to do with projectile motion

Hey!

There's actually fairly little prep you can do for a practical task like the one you've described. Be familiar with the way in which an experiment is written up (aim, hypothesis, equipment, method, results, discussion, conclusion). Understand how best to write a method (past tense, numbers etc.). Think about the importance of accuracy, reliability, and validity to an experimental design, and feel comfortable in assessing each of these components for a given experiment. That's really the only guidance I can give!

Jake

[jamonwindeyer]

for my first hsc assessment we have a physics prac
and the notification gave very limited info regarding what we will be tested on
(it only said the unit of "space")
its worth 25% which is quite a bit, however this is only my second practical test in science.

advice on how to study and does anyone have any practice papers for pracs so i could possibly
carry it out at home? my intuition tells me it could have something to do with projectile motion

Only addition I'd make to above is maybe to smash out a few projectile motion questions? Just a handful of the typical ones to make sure you know the formulae to use for specific situations but yeah, there isn't a whole lot you can do for prep here. That said, if you go here you'll see a few sample assessment tasks from Hurlstone for Term 4; they could match slightly to what you'll get in your Prac! They seem like half Prac half theory though good luck!

[FallonXay]

for my first hsc assessment we have a physics prac
and the notification gave very limited info regarding what we will be tested on
(it only said the unit of "space")
its worth 25% which is quite a bit, however this is only my second practical test in science.

advice on how to study and does anyone have any practice papers for pracs so i could possibly
carry it out at home? my intuition tells me it could have something to do with projectile motion

My school did a practical exam for physics (we built a ramp, put it on top of a lab bench and had to work out where to place a cup on the ground so that a marble would roll in). The exam involved this practical aspect, then also a short theoretical paper/exam involving analysis of the pendulum experiment that investigates acceleration due to gravity. Unfortunately, I don't have my exam anymore to show you sample questions but things that were tested included ways to improve/check validity, reliability and accuracy and experimental write up - as Jake mentioned. Also, make sure you're able to identify independent, dependent and controlled variables. We were also tested on relevant aspects to the experiment such as Galileo's interpretation of projectile motion (i.e horizontal and vertical components are independent, the horizontal component was constant and the vertical was equal to the acceleration due to gravity, trajectory of a parabola) and there were aspects involving graphical analysis of projectile motion (and the pendulum experiment); testing skills such as interpreting (or drawing) graphs are a popular question - remember things like labelling graphs and line of best fit.

[katnisschung]

ok so probably a stupid question and im overthinking it but
i can't wrap my head around this...

so i was revising "g-forces" and my teacher was like accelerating up
is the same as decelerating down as both result in g-forces more than 1G.

but waht!!? i get the first and the second situation i get (like u feel it in an elevator) but i cannot
see the second situation mathematically...

[jakesilove]

ok so probably a stupid question and im overthinking it but
i can't wrap my head around this...

so i was revising "g-forces" and my teacher was like accelerating up
is the same as decelerating down as both result in g-forces more than 1G.

but waht!!? i get the first and the second situation i get (like u feel it in an elevator) but i cannot
see the second situation mathematically...

So, if you accelerate up (ie. speed up), it's like when you're in a stationary elevator and it starts going up. There are clear g-forces, because you feel 'pressed' into the ground, and the acceleration is clearly up. How do we tell? Well, initially your velocity is zero, then it's one, then it's 3, then it's 6 etc. Clearly, your change in velocity is increasing in the upwards direction.

If you decelerate down (ie. 'slow down' when you're travelling downwards), it's like when you're in an elevator travelling downwards, and it slows down to stop. There are also clear g-forces, because you feel 'pressed' into the ground again (suggesting that the g-forces will be exactly the same!). But how can we confirm this mathematically? Well, initially you are travelling downward with a velocity of 6. We can say, then, that you're travelling at -6. Then, you're travelling at -3, then -1, then 0. Clearly, your change in velocity is increasing, also in the upward direction, because you're getting less negative!

Does that make sense?

Jake

[katnisschung]

I GOT IT!
i don't know why but i was thinking of velocity and subbing that in instead
of change of acceleration which is positive the last sentence really helped 
Thanks!

[jakesilove]

I GOT IT!
i don't know why but i was thinking of velocity and subbing that in instead
of change of acceleration which is positive the last sentence really helped 
Thanks!

No problem It's definitely a difficult concept, and was actually involved in one of the trickier multiple choice questions in the 2016 HSC paper!

[katnisschung]

hi im back again....

so im pretty hopeless at maths and i was revising Kepler's laws
by deriving them....

i understand the law (equating centripetal force with gravitational force
and i am able to derive v=...and r^3/T^2)

But where the hell did this derivation come from....
would anyone be able to run me through the steps?
i know its probably fairly simple but like i said im terrible at maths

[RuiAce]

hi im back again....

so im pretty hopeless at maths and i was revising Kepler's laws
by deriving them....

i understand the law (equating centripetal force with gravitational force
and i am able to derive v=...and r^3/T^2)

But where the hell did this derivation come from....
would anyone be able to run me through the steps?
i know its probably fairly simple but like i said im terrible at maths

[katnisschung]

thanks ruiace yeah i understood that
but where did the formula i attached come from?
how do you equate the period of the first planet's orbit to the
period of the second planets orbit...

hope i've expressed myself more clearly