Physics: Post your doubts here!

[amal sharkawi]

Can anyone answer this plz
Why the answer is D ????

 

[fantastic girl]

we take the magnitude
and then we understand it by either work done BY gas or work done ON gas

i dont get it bro
why cnt i use the formula ? :/
isnt the work being done ON the system here ?

 

[Xylferion]

How to calculate the angles?

The question is about diffraction gratings, so you need to recall the formula d sin theta = n lambda

d is the slit separation, which in this question it is 2.00 micrometers giving 2.00 x 10^-6 meters.
sin theta is what you're going to use to find the angle between the orders.
n = order number
lambda = wavelength

To find the angle separation, you subtract the angle for the first order from the angle of the second order.

For the first angle,
2.00 x 10^-6 ( Sin theta ) = 1 ( 600 x 10^-9)
Sin theta = 0.3
Theta = Sin^-1 ( 0.3)
Theta = 17.45

For the second angle,
2.00 x 19^-6 ( Sin theta ) = 2 ( 600 x 10^-9)
Sin theta = 0.6
theta = Sin^-1 ( 0.6)
theta = 36.86

Angle separation = 36.86 - 17.45 = 19.4(1)

 

[fantastic girl]

we are using the formula, but are only taking the magnitude

owkay.
can u tell me why we arent taking the sign into consideration?

 

[Xylferion]

can someone solve the first question of variant 2/o/n/ 2014 paper 2 and show me your working

Not sure if you want the whole of question 1, but I'll just explain the first part for now.

For part (a),

The Young's modulus of a metal wire is 1.8 × 10^11 Pa
Young's modulus is defined as stress/ strain.
You're given the strain which is 8.2 × 10^–4.

They want the stress, in giga pascals. giga being 10^9

First find the stress, this will be 1.8 x 10^11 * 8.2 x 10^-4.
Which is 147,600,000 Pascals.

1 pascal = 10^-9 giga pascals since it's / 10^-9.
147,600,00 pascals = 0.1476 GPa.
You can round this up if you want, to either 0.15 or 0.148. I'd recommend 3 significant figures.

Hope that helped

 

[fantastic girl]

it's already said work done ON gas.
+work done is energy and is a scalar.
a negative energy has on meaning

oh
thanks alot

 

[Ahmed Aqdam]

View attachment 51978
Can anyone answer this plz
Why the answer is D ????

Total resistance is 6Ω. Emf is E.
pd across 2Ω resistor is 2/6E and 4Ω resistor is 4/6E.
At X potential will be E which is maximum and after 2Ω resistor it will be 4/6E. So the latter part of the graph will be steep as it has more resistance and so more potential difference too.

 

[Xylferion]

I meant that the weight is balanced by some force first and only then the resultant force produces acceleration. I think you misinterpreted or maybe I didn't convey it properly.

No no no no....... You're misunderstanding the concept of resultant forces and what the question is asking of you.

A resultant force does NOT require the weight to be balanced in THIS question. They did not mention anything besides the mass. They did not mention where the object is, what direction the force is acting in, all they said was that there is a resultant force.

They told us there clearly, the objects starts from "rest". Then a force is applied to this "still" object, which makes it accelerate in the direction of the resultant force.
It does not depend on the weight being balanced in order to exist, that is completely false. If the weight is balanced, and the object is not moving, the resultant force would be zero and in the end there won't be any acceleration.

Let me show you a hypothetical situation,

Then a force is applied to the object, perhaps friction resists that?

Force = mass x acceleration, NOT weight x acceleration.
Both these forces here, are dependent on the mass.


This should be considered, but in THIS question, it's irrelevant. We are not required to consider it.

Hope that made sense

 

[Dynamite]

fantastic girl smthing like this

 

[fantastic girl]

View attachment 51993
fantastic girl smthing like this

Thanks alot

 

[zain ul abidin]

O/N 10 43 Q3 (b)

 

[Saad ur rehman]

May June 2008 Q6 part b) , Please Explain the combinations,
1)Closed,Closed,Open
2)Closed,Closed,Closed
Will the Current be divided at the S2 switch? I believe it will but how do i Calculate it???

 

[Saad ur rehman]

check at
http://physics-ref.blogspot.com/2014/11/physics-9702-doubts-help-page-8.html

THNX MATE!

 

[smhfifa]

no idea u can use http://maxpapers.com/

Thanks

 

[Physux]

No no no no....... You're misunderstanding the concept of resultant forces and what the question is asking of you.

A resultant force does NOT require the weight to be balanced in THIS question. They did not mention anything besides the mass. They did not mention where the object is, what direction the force is acting in, all they said was that there is a resultant force.

They told us there clearly, the objects starts from "rest". Then a force is applied to this "still" object, which makes it accelerate in the direction of the resultant force.
It does not depend on the weight being balanced in order to exist, that is completely false. If the weight is balanced, and the object is not moving, the resultant force would be zero and in the end there won't be any acceleration.

Let me show you a hypothetical situation,
View attachment 51988
Then a force is applied to the object, perhaps friction resists that?
View attachment 51989
Force = mass x acceleration, NOT weight x acceleration.
Both these forces here, are dependent on the mass.

View attachment 51990
This should be considered, but in THIS question, it's irrelevant. We are not required to consider it.

Hope that made sense

That surely makes sense but sadly you're not getting what I'm trying to say.

 

[Autumngirl]

Can someone please explain in detail how to solve question 3 part b of ON 2010 paper 43 I just can't seem to get it!

 

[Xylferion]

That surely makes sense but sadly you're not getting what I'm trying to say.

What are you trying to say?

 

[TheJDOG]

Hey you all! How's everyone lately? I'm back here really missed helping people in physics. Physics <3

 

[TheJDOG]

Hello guys, could someone please help me in this one, I tried reading the marking scheme multiple times but it didn't help at all.
I am unable to solve 9b
I would appreciate a clear explanation ^_^ THANKS!
Paper: 9702/s09/qp4 Question 9b, page 16

View attachment 51920

Ok bro, just solved this for you.
Read carefully
9a)i) they want the mean activity of the sample, the mean activity is change in N/change in t
Where N is the nuclei at time t.
ii) probability of decay of a nucleus is the change in N / N

b) Given : cobalt-60 source half life: 5.27 years
Activity: 3.50 x 10^5 Bq unceraitiny is +-2%

Calculate the time in days for the activity to have a maximum possible error of 10%.
10% - 2%= 8%
Well, the activity possible error must be 8% because the uncertainty must not exceed 10%
We know that A=Aoexp(-lambdat) and that lambda= ln2/T1/2
We have to find A, the activity after time t, which here is = Ao - (A0 x 8/100) where Ao is initial activity
A= 3.50 x 10^5 - (3.50 x 10^5 x 8/100)= 3.22 x 10^5
Lambda is = ln2/5.27=0.132

Now substitute and work for time

3.22x10^5= 3.50x10^5 exp(-ln2/5.27 x t)
0.92= exp(-0.132t)
ln0.92= -0.132t
t= 0.634 years which is 230 days
Note keep lambda on your calculator as ln2/5.27 for an accurate answer

 

[Bba321]

Hey please explain me qs 9 part bii of October November 2013/43

Thanks