February 17, 2020, 02:03:08 pm

0 Members and 2 Guests are viewing this topic.

#### HolHen

• Posts: 6
• Shine on <3
• Respect: +1
##### Re: VCE Physics Question Thread!
« Reply #2235 on: February 09, 2019, 05:49:48 pm »
0
What are some topics to watch out for in Physics 1/2?

TBH I found most of the topics in 1/2 okay once I took some time to understand them.
Some of the ones that were a little tricky were specific and latent heat in thermodynamics (especially the questions that ask you to find the final temperature when adding ice etc. to a solution); potential spring energy; some of the rollercoater energy conversion questions; and radioisotopes.

Hope that helps good luck
2018:
2019:
Methods [44]   Spec [50]  Physics [42]   Japanese SL [43]   English [40]

#### mcl0028

• Fresh Poster
• Posts: 4
• Respect: 0
##### Re: VCE Physics Question Thread!
« Reply #2236 on: February 11, 2019, 10:08:31 am »
0
I dont get the difference between electric and magnetic feilds or electricity and magnetism in terms of fundamental principles and why there is another phenomena called magnetism and not just electricity. I understand it terms of special relativity and that helped make distinuishes for moving particles but how do dipoles exist etc. noone has been able to describe the magnetic phenomena to me and my teacjer just said "i cant answer that" pls help ded. i understand elctricity as the effect of charged particles

#### lzxnl

• Victorian
• ATAR Notes Legend
• Posts: 3430
• Respect: +209
##### Re: VCE Physics Question Thread!
« Reply #2237 on: February 11, 2019, 09:25:41 pm »
+4
I dont get the difference between electric and magnetic feilds or electricity and magnetism in terms of fundamental principles and why there is another phenomena called magnetism and not just electricity. I understand it terms of special relativity and that helped make distinuishes for moving particles but how do dipoles exist etc. noone has been able to describe the magnetic phenomena to me and my teacjer just said "i cant answer that" pls help ded. i understand elctricity as the effect of charged particles
Well...you can't actually distinguish between electricity and magnetism because they're related, as you've mentioned, by special relativity. Indeed, they're part of a more unified object called the electromagnetic field tensor which I won't go into here.

Maxwell's equations for electromagnetism tell us that electric fields are generated by charges and magnetic fields are generated by currents. However, there is one other source of magnetism too that indirectly enter into Maxwell's equations:
Elementary particles have an inherent magnetic dipole moment, which is best thought of as being spinning magnets. These dipole moments have directions, so if you line up all of these elementary particle dipole moments, you get a magnet. This is how permanent magnets work, and probably what you're thinking of when you ask for how dipoles exist.
2012
Mathematical Methods (50) Chinese SL (45~52)

2013
English Language (50) Chemistry (50) Specialist Mathematics (49~54.9) Physics (49) UMEP Physics (96%) ATAR 99.95

2014-2016: University of Melbourne, Bachelor of Science, Diploma in Mathematical Sciences (Applied Maths)

2017-2018: Master of Science (Applied Mathematics)

2019-:

Accepting students for  VCE tutoring in Maths Methods, Specialist Maths and Physics! PM for more details

#### dream chaser

• Forum Obsessive
• Posts: 250
• Respect: +1
##### Re: VCE Physics Question Thread!
« Reply #2238 on: February 16, 2019, 10:44:58 am »
0
Hi Guys,

Got a few questions I want answered. Look at the diagrams in the attachments when answering them. I know it is not part of the VCAA study design(I think) but will help me understand the topic better. By the way, for the vertical loop to loop diagram, assume that the object is at the top and bottom of the loop.

Q1. Are there any horizontal forces acting on the object in any of these diagrams. If so, what and in which diagrams.

Q2. In every position of each diagram, is the object travelling at a constant speed. If so, which one.

Q3. Do we need to either qualitatively and/or quantitatively about the motion of objects in the diagrams given when they are not at the top or at the bottom?

All help and replies will be very much appreciated. Thanks.
« Last Edit: February 16, 2019, 10:59:34 am by dream chaser »

#### dream chaser

• Forum Obsessive
• Posts: 250
• Respect: +1
##### Re: VCE Physics Question Thread!
« Reply #2239 on: February 18, 2019, 09:39:37 am »
0
Hi Guys,

Need help with these couple of questions.

Q1. An empty railway cart of mass 500 kg is moving along a horizontal low-friction track at a velocity of 3.0 m s−1 due south when a 250 kg load of coal is dropped into it from a stationary container directly above it.

(a) Calculate the velocity of the railway cart immediately after the load has been emptied into it.

(b) What happens to the vertical momentum of the falling coal as it lands in the railway cart?

(c) If the fully loaded railway cart is travelling along the track at the velocity calculated in (a) and the entire load of coal falls out through a large hole in its floor, what is the final velocity of the cart?

Q2. Two iceskaters, Melita and Dean, are performing an ice dancing routine in which Dean (with a mass of 70 kg) glides smoothly at a velocity of 2.0 m s−1 due east towards a stationary Melita (with a mass of 50 kg), holds her around the waist and they both move off together. During the whole move, no significant frictional force is applied by the ice.

(a) What is Dean’s momentum before making contact with Melita?

(b) Where is the centre of mass of the system comprising Dean and Melita 3.0 s before impact?

(c) What is the velocity of the centre of mass of the system before impact?

(d) Calculate the common velocity of Melita and Dean immediately after impact.

(e) What impulse is applied to Melita during the collision?

For question 1, how are we meant to solve (a)? I used m1u1 + m2u2 = The sum of m x v, however don't know what u2 given that 1 is for the railway cart and 2 is for the coal. We need u2 to solve for v. How do I do it?

For question 2, I don't get what question (b) is asking for. What do they mean 'where is the centre of mass comprising Dean and Melita'? And for (c), are they just asking for the combined velocity before impact?

I don't want anyone to answer all the questions on this post for me, just the parts from the last 2 paragraphs above as I am unsure as to how to do it. Once I know how to do it, I should be able to do the rest by myself.

Also, it would be great if someone could answer the questions from my previous post on the physics QandA thread. It will really help me out.

All help, replies and feedback will be very much appreciated. Thanks.
« Last Edit: February 18, 2019, 09:45:32 am by dream chaser »

#### dream chaser

• Forum Obsessive
• Posts: 250
• Respect: +1
##### Re: VCE Physics Question Thread!
« Reply #2240 on: February 21, 2019, 03:30:08 pm »
0
Hi Guys,

Q1. Say for instance there is a block that is held at the end of a spring vertically. At any position(including when it is/is not at equilibrium), will the Tension of the block be equal to the weight.

Q2. Say for instance a car collides with a spring making it compress. Even if it does not compress to its maximum compression, do we suggest that all the kinetic energy gets transferred into elastic potential energy?

All help will be much appreciated. Thanks.

#### Bri MT

• VIC MVP - 2018
• ATAR Notes Legend
• Posts: 3429
• invest in wellbeing so it can invest in you
• Respect: +2484
##### Re: VCE Physics Question Thread!
« Reply #2241 on: February 22, 2019, 03:57:01 pm »
+4
Hey, I'm giving you hints to help you get started since I think you'll probably be okay with a few of them after that. If you still don't really understand feel free to let me know

Set 1
Q1 The two forces we would be considering here (ignoring resistive forces) are weight and the normal force. Remember that the normal force acts perpendicular to the surface the cart/trolley/whatever is on.

Q2 Think of your experiences in regards to speed - then consider how physics could explain this

Q3 is there a verb missing here?

Set 2

Q1.
you're right that you use conservation of momentum . Ignore the vertical velocity of the coal (it'll have 0 once it finishes falling anyway), and use the fact that the coal has 0 horizontal velocity

Q2.
I'm pretty sure it just wants to know their displacement using the velocity and time elapsed

and yeah it just wants the velocity of the Dean and Malta system

Set 3
Q1 Think about when the net force will equal 0

Q2 yeah for any calculation questions you would. If you need to describe things qualitatively you would be expected to know that energy transfers aren't 100% efficient.

Hope this helps!

#### dream chaser

• Forum Obsessive
• Posts: 250
• Respect: +1
##### Re: VCE Physics Question Thread!
« Reply #2242 on: February 23, 2019, 03:02:17 pm »
0
Hey, I'm giving you hints to help you get started since I think you'll probably be okay with a few of them after that. If you still don't really understand feel free to let me know

Set 1
Q1 The two forces we would be considering here (ignoring resistive forces) are weight and the normal force. Remember that the normal force acts perpendicular to the surface the cart/trolley/whatever is on.

Q2 Think of your experiences in regards to speed - then consider how physics could explain this

Q3 is there a verb missing here?

Set 2

Q1.
you're right that you use conservation of momentum . Ignore the vertical velocity of the coal (it'll have 0 once it finishes falling anyway), and use the fact that the coal has 0 horizontal velocity

Q2.
I'm pretty sure it just wants to know their displacement using the velocity and time elapsed

and yeah it just wants the velocity of the Dean and Malta system

Set 3
Q1 Think about when the net force will equal 0

Q2 yeah for any calculation questions you would. If you need to describe things qualitatively you would be expected to know that energy transfers aren't 100% efficient.

Hope this helps!

Cheers miniturtle for the reply. Much appreciated.

For Set 1 Q3, the verb missing was know.

And for Set 3 Q1, would that mean that only at equilibrium where the fnet would be 0N?

#### Bri MT

• VIC MVP - 2018
• ATAR Notes Legend
• Posts: 3429
• invest in wellbeing so it can invest in you
• Respect: +2484
##### Re: VCE Physics Question Thread!
« Reply #2243 on: February 24, 2019, 10:43:58 am »
+5
Cheers miniturtle for the reply. Much appreciated.

For Set 1 Q3, the verb missing was know.

And for Set 3 Q1, would that mean that only at equilibrium where the fnet would be 0N?

Set 1 Q3 We don't need to know about anything other than the top and the bottom (see page 39 of the study design) - but you might find a qualitative understanding useful for "getting" the topic.

Set 3 Q1  We know the upwards force being applied to the block is from the tension in the spring, and the downwards force is the weight of the block. When they equal, they'll cancel eachother out (Fnet = 0) and the acceleration will be zero. Yes, this is the case when the block is at the equilibrium position. Let's look at a few ways of thinking about this.
- At the equilibrium position, the kinetic energy is at a maximum because speed is at a maximum too. When the velocity is at a stationary point (eg a maximum or minimum), the acceleration is 0
- At the equilibrium position, the displacement from that position is zero: F=-kx, F=-k(0), F=0

If the spring being vertical is confusing you, this is a video I found useful when I was in VCE

If you think about Hooke's law, it wouldn't make sense for Fnet to be zero at any other time given that weight is constant

#### dream chaser

• Forum Obsessive
• Posts: 250
• Respect: +1
##### Re: VCE Physics Question Thread!
« Reply #2244 on: February 24, 2019, 02:50:59 pm »
0
Set 1 Q3 We don't need to know about anything other than the top and the bottom (see page 39 of the study design) - but you might find a qualitative understanding useful for "getting" the topic.

Set 3 Q1  We know the upwards force being applied to the block is from the tension in the spring, and the downwards force is the weight of the block. When they equal, they'll cancel eachother out (Fnet = 0) and the acceleration will be zero. Yes, this is the case when the block is at the equilibrium position. Let's look at a few ways of thinking about this.
- At the equilibrium position, the kinetic energy is at a maximum because speed is at a maximum too. When the velocity is at a stationary point (eg a maximum or minimum), the acceleration is 0
- At the equilibrium position, the displacement from that position is zero: F=-kx, F=-k(0), F=0

If the spring being vertical is confusing you, this is a video I found useful when I was in VCE

If you think about Hooke's law, it wouldn't make sense for Fnet to be zero at any other time given that weight is constant

Thanks Miniturtle. Really appreciate the help.

#### huangggygy

• Fresh Poster
• Posts: 2
• Respect: 0
##### Re: VCE Physics Question Thread!
« Reply #2245 on: February 26, 2019, 09:09:35 pm »
0
If 0.20 kg of water at 90 C is mixed with 0.50 kg of water at 16 C, what is the final
temperature of the mixture?

If 100 g of water at 95 C is poured into a 500 g glass cup (with an initial temperature of 25
C), what is the final temperature of the water and the cup? (specific heat capacity of
glass = 8.42 × 10 2 J kg -1 K -1 ).

thanks ^^ need help on these two

#### lzxnl

• Victorian
• ATAR Notes Legend
• Posts: 3430
• Respect: +209
##### Re: VCE Physics Question Thread!
« Reply #2246 on: February 26, 2019, 10:02:00 pm »
+2
If 0.20 kg of water at 90 C is mixed with 0.50 kg of water at 16 C, what is the final
temperature of the mixture?

If 100 g of water at 95 C is poured into a 500 g glass cup (with an initial temperature of 25
C), what is the final temperature of the water and the cup? (specific heat capacity of
glass = 8.42 × 10 2 J kg -1 K -1 ).

thanks ^^ need help on these two
For the first question, let the final temperature be x degrees C, where 16 < x < 90. Then, the 0.2 kg of water transfers a certain amount of heat to the 0.5 kg water, given by the specific heat capacity * mass * temperature change (90 - x). This heat transferred is the same as the heat used to heat the 0.5 kg water, which is specific heat capacity * mass * temperature change (x - 16). Basically, the temperature change is inversely proportional to the mass. See what you get.

Do the same for the second problem, except now the specific heat capacities are different.
2012
Mathematical Methods (50) Chinese SL (45~52)

2013
English Language (50) Chemistry (50) Specialist Mathematics (49~54.9) Physics (49) UMEP Physics (96%) ATAR 99.95

2014-2016: University of Melbourne, Bachelor of Science, Diploma in Mathematical Sciences (Applied Maths)

2017-2018: Master of Science (Applied Mathematics)

2019-:

Accepting students for  VCE tutoring in Maths Methods, Specialist Maths and Physics! PM for more details

#### schoolstudent115

• Trailblazer
• Posts: 27
• Year 10: Physics
• Respect: 0
##### Re: VCE Physics Question Thread!
« Reply #2247 on: March 02, 2019, 02:11:02 pm »
0
If each LED is identical, and each have a switch-on voltage of $V_s=20$mA, then what resistance $R_L$ is required for the LED's to have optimal light production?
I have tried working out that given the voltage difference is equal across the circuit, resistance is equal to: 2/0.06, as the total current must be 3 times 20 milliamps - This was apparently wrong.
In the same question , there was the same circuit, except the led's were in series, and I got the correct answer.
(2019) Year 10: Physics

#### lzxnl

• Victorian
• ATAR Notes Legend
• Posts: 3430
• Respect: +209
##### Re: VCE Physics Question Thread!
« Reply #2248 on: March 02, 2019, 09:45:37 pm »
0
If each LED is identical, and each have a switch-on voltage of $V_s=20$mA, then what resistance $R_L$ is required for the LED's to have optimal light production?
I have tried working out that given the voltage difference is equal across the circuit, resistance is equal to: 2/0.06, as the total current must be 3 times 20 milliamps - This was apparently wrong.
In the same question , there was the same circuit, except the led's were in series, and I got the correct answer.

You mean switch on voltage of 20 mV? mA is not a unit of voltage.
2012
Mathematical Methods (50) Chinese SL (45~52)

2013
English Language (50) Chemistry (50) Specialist Mathematics (49~54.9) Physics (49) UMEP Physics (96%) ATAR 99.95

2014-2016: University of Melbourne, Bachelor of Science, Diploma in Mathematical Sciences (Applied Maths)

2017-2018: Master of Science (Applied Mathematics)

2019-:

Accepting students for  VCE tutoring in Maths Methods, Specialist Maths and Physics! PM for more details

#### Srivathsa

• Fresh Poster
• Posts: 1
• Respect: 0
##### Re: VCE Physics Question Thread!
« Reply #2249 on: March 10, 2019, 01:42:45 pm »
0
Hey goiz, I got a quick question,
Why is the electric field between two parallel charged plates uniform? I mean I get that their field lines are parallel, but why are they even parallel?
Also why does the field line curve outwards at the ends of the plates?