Login

Welcome, Guest. Please login or register.

March 29, 2024, 07:15:35 am

Author Topic: QCE Physics Questions Thread  (Read 23480 times)

0 Members and 2 Guests are viewing this topic.

jinx_58

  • Trendsetter
  • **
  • Posts: 143
  • "I am not afraid to walk this world alone" - MCR
  • Respect: +22
Re: QCE Physics Questions Thread
« Reply #60 on: September 18, 2021, 03:58:23 pm »
0
Howdy.

I was looking through Unit 2 content and found this problem:
A child seating in a rowing boat initially at rest throws a package of mass 5kg out of the back with a speed of 10m/s. Determine the speed and direction of the boat immediately after the package was released if the child weighs 24kg and the boat weighs 40kg.

I have attached the working I've done so far.

Could someone please help?
- jinx_58
Class of 2022!
Currently doing Unit 4: QCE
Physics || Chemistry ||Methods || General English || Ancient History || Religion & Ethics
My Year 12 QCE Journal!

noor.fatimaaa

  • Fresh Poster
  • *
  • Posts: 4
  • Respect: 0
Re: QCE Physics Questions Thread
« Reply #61 on: September 19, 2021, 03:49:45 pm »
0
Hello
Does an anyone know what I can write in my rationale
I am working on a physics IA2 and the experiemtn is on the angle of a ramp and the displaceemnts affect on time
My teacher has told me to research about a theory and put it in my rationale. Which theory can i use? What else can i write about in my rationale?
Please help

Gracey1415

  • Fresh Poster
  • *
  • Posts: 4
  • Respect: 0
Re: QCE Physics Questions Thread
« Reply #62 on: October 09, 2021, 11:51:33 am »
0
question reguarding distance between an electric field and charges.
I have no idea how to figure out the distance x here, any help would be appreciated :)
I have attached the question and the answer is supposed to be 1m but idk how

K.Smithy

  • QLD MVP - 2019
  • Moderator
  • Forum Obsessive
  • *****
  • Posts: 400
  • "We are the cosmos made conscious." B.C. (she/her)
  • Respect: +396
Re: QCE Physics Questions Thread
« Reply #63 on: October 09, 2021, 12:11:42 pm »
+4
question reguarding distance between an electric field and charges.
I have no idea how to figure out the distance x here, any help would be appreciated :)
I have attached the question and the answer is supposed to be 1m but idk how

Hey Gracey1415!
If you get a question like this where you are finding the electric field strength at a given point due to multiple sources, then you will need to do a superposition of the electric field (essentially combining the electric fields produced by either source).
In this case, you are able to do a simultaneous equation implementing the expressions for the electric fields resulting from each point charge - then you can just solve for x.

Here is the working I did to get the answer

Apologies for my terrible trackpad writing ahaha.

I hope this working out makes sense, but feel free to give us a shout if you are still having some trouble with it and I'd be more than happy to help out a bit more :)
Katelyn
« Last Edit: October 09, 2021, 12:18:53 pm by K.Smithy »
QCE 2020: Physics (92) || Psychology (96) || Biology (93) || Methods (79) || English (98) || SOR (91)
ATAR: 98.40
2021-2024: Bachelor of Advanced Science (Honours) @ UQ

Uni Journal ; U3 Bio ; U3 Psych ; U3 Physics

Gracey1415

  • Fresh Poster
  • *
  • Posts: 4
  • Respect: 0
Re: QCE Physics Questions Thread
« Reply #64 on: October 09, 2021, 01:05:51 pm »
0
Hey Gracey1415!
If you get a question like this where you are finding the electric field strength at a given point due to multiple sources, then you will need to do a superposition of the electric field (essentially combining the electric fields produced by either source).
In this case, you are able to do a simultaneous equation implementing the expressions for the electric fields resulting from each point charge - then you can just solve for x.

Here is the working I did to get the answer
(Image removed from quote.)
Apologies for my terrible trackpad writing ahaha.

I hope this working out makes sense, but feel free to give us a shout if you are still having some trouble with it and I'd be more than happy to help out a bit more :)
Katelyn

Thanks so much!
Why should you disregard the negative for the 18 coulombs?

K.Smithy

  • QLD MVP - 2019
  • Moderator
  • Forum Obsessive
  • *****
  • Posts: 400
  • "We are the cosmos made conscious." B.C. (she/her)
  • Respect: +396
Re: QCE Physics Questions Thread
« Reply #65 on: October 09, 2021, 01:23:56 pm »
+4
Thanks so much!
Why should you disregard the negative for the 18 coulombs?

When you use formulae such as this one and Coulomb's law, you're interested in the magnitude of the electric field strength or the magnitude of the force. So, if you had a Coulomb's law question and you had one point charge of 2 µC separated from a second point charge of -2 µC by a distance of 2 m, then you would disregard the negative in your calculations for the magnitude of the force.
So you would have
F = ((9*109)(2*10-6)(2*10-6))/22

Rather than having a negative 2 for one of the Qs
F = ((9*109)(2*10-6)(-2*10-6))/22

This is because we are simply interested in the magnitude of the force (which will always be presented as a positive number). The signs of the charges will tell us whether the force between the charges will be attractive or repulsive. In this case, we know that the force between them will be attractive. This is because Coulomb's law tells us the opposite charges attract.

Similarly, when we are working with electric field strength we are interested in the magnitude. So we can leave the negative off of the -18µC charge. All it tells us is that the electric field from the negative point charge will oppose that of the positive 2µC point charge. Meaning they will cancel out. If you put the negative in the calculation, then when you do your simultaneous equation the will add together (instead of cancel out) and you will get the wrong answer for distance.

I hope this makes a little more sense :)
QCE 2020: Physics (92) || Psychology (96) || Biology (93) || Methods (79) || English (98) || SOR (91)
ATAR: 98.40
2021-2024: Bachelor of Advanced Science (Honours) @ UQ

Uni Journal ; U3 Bio ; U3 Psych ; U3 Physics