VCE Physics Question Thread!

[skrt skrt]

Thats a parabolic path. If you go to 2014 Q3 b), the path is stopped by an advertising board.
So you wouldn't double the time.

[KiNSKi01]

I have no clue what this question is on about or how to visualise it:
"An electron moves due North in a horizontal plane with uniform speed. It enters a uniform field directed due South in the same plane. Which one of the following statements concerning the motion of the electron in the magnetic field is correct?'
Answer= It continues to move North with its original speed

Help please 

[Bri MT]

I have no clue what this question is on about or how to visualise it:
"An electron moves due North in a horizontal plane with uniform speed. It enters a uniform field directed due South in the same plane. Which one of the following statements concerning the motion of the electron in the magnetic field is correct?'
Answer= It continues to move North with its original speed

Help please 

Start out by drawing a diagram. Mark "up" on your page as north and draw the electron with an arrow pointing upwards. Then draw the field lines running south.

Notice that the electron is moving parallel to the field lines; therefore the field lines will have no impact on the electrons motion

[KiNSKi01]

thanks miniturtle!! makes sense now 

got confused by the wording of the question

[DrDin]

Hello everyone! I have a special relativity question that I can't wrap my head around. Particularly part d). An answer with an explanation will be much appreciated. Thanks!

[Yertle the Turtle]

Hello everyone! I have a special relativity question that I can't wrap my head around. Particularly part d). An answer with an explanation will be much appreciated. Thanks!

Hey there, welcome to ATAR Notes!
The speed of sound varies depending on your speed relative to it. Therefore in these questions you would find your speed relative to the source of the sound and then add/subtract from the speed of sound.
Hope this helps

[DrDin]

Hey there, welcome to ATAR Notes!
The speed of sound varies depending on your speed relative to it. Therefore in these questions you would find your speed relative to the source of the sound and then add/subtract from the speed of sound.
Hope this helps

Thanks for the welcome!
Yep that makes sense. But the for the last one I don't get the correct answer (I may be misinterpreting the question). The answer is apparently 340ms^-1. I don't understand why the speed relative to sound in this case is 0.

[Shadowxo]

Thanks for the welcome!
Yep that makes sense. But the for the last one I don't get the correct answer (I may be misinterpreting the question). The answer is apparently 340ms^-1. I don't understand why the speed relative to sound in this case is 0.

I think it's because you're about to overtake the fire truck, meaning you're right beside it. The sound waves you hear will be travelling perpendicular to your motion rather than from in front / behind you. This means for this question your speeds don't matter because your left/right velocity is 0.
Hope that makes sense haha

[Richard Feynman 101]

Know the authors of the book.

Answers are incorrect.

[DrDin]

Know the authors of the book.

Answers are incorrect.

Okay? Do you know the correct answer?

I think it's because you're about to overtake the fire truck, meaning you're right beside it. The sound waves you hear will be travelling perpendicular to your motion rather than from in front / behind you. This means for this question your speeds don't matter because your left/right velocity is 0.
Hope that makes sense haha

Your explanation makes a lot of sense. But now I'm confused as the Richard Feynman 101 is saying the answers are incorrect D:

[Seno72]

I'm pretty sure the answers are correct.

[skrt skrt]

Hey people, could someone please explain why Fg=Fc. This reminds of Es=Ek for spring questions(kinetic energy converts to spring potential and vice versa). However I don't see the connection between Fg=Fc, isn't Fc the sum of all force hence its not a real force?

thanks

[Seno72]

Hey people, could someone please explain why Fg=Fc. This reminds of Es=Ek for spring questions(kinetic energy converts to spring potential and vice versa). However I don't see the connection between Fg=Fc, isn't Fc the sum of all force hence its not a real force?

thanks

I think you mean Fnet=Fc (Centripetal force)?  Fnet and Fc are the vector some of multiple forces, sometimes including the Fg.

[Shadowxo]

Hey people, could someone please explain why Fg=Fc. This reminds of Es=Ek for spring questions(kinetic energy converts to spring potential and vice versa). However I don't see the connection between Fg=Fc, isn't Fc the sum of all force hence its not a real force?

thanks

In general this isn't true, but it can be the case for things orbiting the earth, or if something's swinging vertically and is at the top of its swing. What situation is it referring to?

[lzxnl]

Just to address this concept of a 'real force', in F = ma, the ma is not a real force either, yet we can still equate it to a real force, or sum of them.