Physics: Discussion, Questions & Potential Solutions

[jpulvirenti]

any thoughts on a+ cutoff?
higher or lower than last year?

[Theodric_Ironfist]

Why wasnt it 32 N? I thought Block A exerts 4 x 8 N ??

If that were true, then block B would have acceleration 32 x 1 = 32 m/s/s which contradicts the system acceleration of 8 m/s/s/.

[Isopod]

Anyone else struggle with 5d)?

[Seno72]

any thoughts on a+ cutoff?
higher or lower than last year?

I think it would be the same or slightly lower. Overall the questions werent hard like last year. Although the harder questions here were much harder than last years questions. Hopefully a+ cutoff is low 80s but with Physics thats unlikely

[aussiboi]

Anyone else struggle with 5d)?

not sure if its correct this is what i did:
found voltage on transmission side and use V= IR to find current. Thus P = I^2 R not sure if that was correct

[MrTeacherMan]

Anyone else struggle with 5d)?

That was a malformed question. The reader had to assume things such as:

• is the power dissipated in the bulb the same?
• is the power generated by the variable voltage source the same?

The question didn’t have enough information to find an answer without one of these assumptions.

Personally, I think “operate correctly” means that the bulb has a voltage drop of 4 V while also having a current of 12 A as per part a.

Under that assumption, the current in the lines would have been 1.5 A and so power loss would have been 18 W.

[vector_graphics]

Same Did you get 1 meter form centre?!

i got 1 metre. i also thought this was a standing wave question as there was do diffraction/slits present in the diagram/question

[jpulvirenti]

i got 1 metre. i also thought this was a standing wave question as there was do diffraction/slits present in the diagram/question

Heres what i did (in image)
hope i will get at least 1 mark?

[MrTeacherMan]

i got 1 metre. i also thought this was a standing wave question as there was do diffraction/slits present in the diagram/question

As was said before by someone, this is a special case of wave interference (of which standing waves are made from).

If the sound sources are coherent (which we can assume they are), then the peaks from A will reach the centre at the same as the peaks from B, similarly for troughs. Thus at the centre, the two waves should constructively interfere, forming an antinode.

Extend this idea along the line connecting the sources, and you should see that it really is just a path difference situation. Antinodes will occur every 0.5 m from the centre, with nodes in between.

Thus the second node will occur 0.5 + 0.25 = 0.75 m from the centre, in either direction.

[KiNSKi01]

loool vcaa 'tricked' a fair few people with a interference question with sound last year and I reckon they have pulled it off again this year 

[jpulvirenti]

what did you guys get for the 20 hour quazer question?

[izam25]

what did you guys get for the 20 hour quazer question?

I think I got like 14.2 h or something, have a feeling I'm off but

[MrTeacherMan]

I think I got like 14.2 h or something, have a feeling I'm off but

You’d be right. The 20 h period of the quasar is dilated time. If the Lorentz factor was 1.41, then proper time (period according to the quasar) is 20/1.41 = 14.2 h.

[jpulvirenti]

I think I got like 14.2 h or something, have a feeling I'm off but

I believe ur right.
As from the quazers reference, the time for its emission is shorter (time/gamma) gamma was 1.4 or something, which works out to be around 14.8
 

[izam25]

You’d be right. The 20 h period of the quasar is dilated time. If the Lorentz factor was 1.41, then proper time (period according to the quasar) is 20/1.41 = 14.2 h.

Damn, thanks man was so sure I messed up hahaha