Physics: Post your doubts here!

[waqas123]

Can someone explain this to me?

I got it.

1. PE = q x V so V = PE/q
2. E = V/r
thus substitute 1 into 2:
E = PE/qr
3. as G = PE/r, thus E = G/q and Eq = G

 

[Mahnoorfatima]

I think what the question really wants you to say (I could be wrong) is that there are DISTINCT bands in the line spectra. It's not like ALL wavelengths of light were absorbed, but rather distinct, specific ones.

You have to be careful with the wording of the question. They said: "Explain how the line spectrum of hydrogen provides evidence for..."
So you HAVE to talk about the APPEARANCE of the spectrum itself. Hope I'm making sense.

Spoiler

Ummm, if you could tell me please, What would you write?

 

[Mahnoorfatima]

How do I answer this question..? :3 View attachment 60505

qwertypoiu what about this?

 

[nadeen64]

Can someone please try these two questions and explain how to do them? Both of them are C.

 

[i_try9621]

Doubt in Q 4) b) ii). I checked the Markscheme and they tell me to count the boxes, is there any other way to calculate the Energy Es? from http://papers.gceguide.com/A Levels/Physics (9702)/9702_w10_qp_22.pdf

 

[nadeen64]

Hii, can someone please help with question 5 in paper 21 nov 2015??

 

[princess Anu]

Someone help
Ans is 1.5
Why is my ans coming wrong

 

[Aishayasin]

Can Anyone Help me with

Answer is B how?

 

[Aishayasin]

A ball is thrown vertically downwards at 4.0 m/s from a height of 120 cm .With which speed does it hit the ground? Ignore air resistance.
A 4.8 m/s B 6.3 m/s C 40 m/s D 49 m/s
Answer is B

 

[Aishayasin]

Someone help
Ans is 1.5
Why is my ans coming wrongView attachment 60535

If it takes 12 hours to go from low tide to high tide and back to low tide, that means it takes 12 hours to go from 1.0m, to 3.0m and back to 1.0m.

So in half of 12 hours= 6 hours it goes from 1 to 3
And in half of that= 3 hours it goes from 1 to 1.5.

Try drawing a wave starting from the lowest point (1.0m) going to the highest point (3.0m) and coming back to the lowest point (1.0m).
Draw a line through where it is 1.5m, which is half way between 1m and 3m. If the whole wave is 12 hours you will see that at a quarter of twelve hours the wave crosses the line you drew for 1.5m

 

[ahmedish]

if we get 14.6 on analogue, when we sample it, do we round up or down?
my teacher says down
my book says nearest number
think i solved an exam where it was nearest number and not down

 

[farhan141]

14.6 is near to 15 so 15.

 

[farhan141]

if we get 14.6 on analogue, when we sample it, do we round up or down?
my teacher says down
my book says nearest number
think i solved an exam where it was nearest number and not down

 

[ahmedish]

lol my teacher is so bad

 

[farhan141]

lol my teacher is so bad

Happens

 

[ahmedish]

Happens

which p4 did u take

 

[farhan141]

42

 

[i_try9621]

Anyone help me with this question? Ans for this is B.

 

[i_try9621]

see solution 64 at
http://physics-ref.blogspot.com/2014/11/physics-9702-doubts-help-page-12.html

I did, but what I don't get it is, as quoted from the blog "Since the mass of the water is spread all over the volume it occupies, the centre of mass should be considered when calculating the (gravitational) potential energy." Why do they consider the centre of mass ? Do we generally consider the centre of mass while considering the Potential energy of an object?

 

[i_try9621]

we always consider the centre of mass. else we would have to calculate the potential eenrgy of each molecule since their positions (height) are each different

Ah! Thanks!