Physics: Post your doubts here!

[Xtreamer]

Can anyone explain this:

Question 81: [Young modulus]
Elastic material with Young modulus E is subjected to tensile stress S. Hooke’s Law is obeyed.
What is the expression for elastic energy stored per unit volume of material?
A S2 / 2E B S2 / E C E / 2S2 D 2E / S2

Reference: Past Exam Paper – June 2014 Paper 13 Q23



Solution 81:
Answer: A.
Elastic energy = ½ Fx
Elastic energy per unit volume = (½ Fx) / V

[Volume V = AL] Elastic energy per unit volume = (½ Fx) / AL.
[F / A = S] Elastic energy per unit volume = Sx / 2L

[Strain = x / L] Elastic energy per unit volume = S {strain} / 2
[Young modulus, E = stress S / strain. So, strain = S / E]

Elastic energy per unit volume = SS / 2E = S2 / 2E

SOURCE: http://physics-ref.blogspot.com/2014/11/physics-9702-doubts-help-page-15.html

 

[asadalam]

I just did this one the Ans is A.....I think current wont pass there because there is a shorter route of less resistance available

View attachment 54952
try this one.

The answer to this question can be reasoned by the symmetry of the circuit.
Current flows from the positive terminal of the battery.
At the left junction, the current divides to flow through the 2 resistors and since the resistances of the resistors are equal, the same current flows through each of them. So, the potential difference across each resistor is the same.
Therefore, the potential at the top junction and the potential at the bottom junction of the 40Ω resistor are the same – that is, the potential difference across the 40Ω resistor is zero.
Thus, no current flows through the 40Ω resistor.
^From Phy Ref
So in other words its like the potentiometer.No PD so no current will flow.

 

[Xtreamer]

Answer is A how???

 

[Abdul Hanan]

View attachment 54956
Answer is A how???

initial mometum o.oo5x200=1Nm
m1v1=m2v2
1=0.1*v2
v2=10m/s
equation of motion 2sa=v^2-u^2
put values your answer will be 5.096m

 

[ryanfarooqi]

View attachment 54956
Answer is A how???

Bro i really wanna help you but i can't upload the pic for it :,(

 

[Ahmed Aqdam]

Good luck everyone!

 

[Xtreamer]

Good luck everyone!

Thanks!

Bro i really wanna help you but i can't upload the pic for it :,(

I Got It buddy! XD

 

[Xtreamer]

Anyone knows how to use time properly for this paper???...i think I will do easy ones first

 

[Xtreamer]

How was the paper???

 

[awesomaholic101]

How was the paper???

Was gonna ask same thing ... I wrote 12, wbu? ... it was easier than last year papers ...
Went pretty well Alhamdulillah but gt mite be high

 

[Boss201]

2(a) (ii) number 2 for acceleration.

From marking scheme :

mg – F = ma hence a = g – [F / m]
m = ρ × V = ρ × 4/3 π R3 = (1.4 × 10–5) C1
a = 9.81 – [6.9 × 10–5] / ρ × 4/3 π × (1.5 × 10–3)3 (9.81 – 4.88) M1
a = 4.9(3) m s–2

How ? and why we got/used this equation mg – F = ma ? why why not mg + f= ma not used ? why the minus sign

 

[Xtreamer]

Was gonna ask same thing ... I wrote 12, wbu? ... it was easier than last year papers ...
Went pretty well Alhamdulillah but gt mite be high

Yep u right gt will be high. I did P12 too. it was very easy for someone who had done pastpapers..CRAM STUDY PAID OFF!
We will discuss it like after that 24 hour thing or whatever

 

[awesomaholic101]

Yep u right gt will be high. I did P12 too. it was very easy for someone who had done pastpapers..CRAM STUDY PAID OFF!
We will discuss it like after that 24 hour thing or whatever

Oh God it sure did!!
24 hrs should be over rite?

 

[Boss201]

Can someone tell me how to measure % uncertainty in a stopwatch

For example i did an oscillation experiment and got time taken 28.05 seconds

how to calculate % uncertainty ?

 

[awesomaholic101]

Can someone tell me how to measure % uncertainty in a stopwatch

For example i did an oscillation experiment and got time taken 28.05 seconds

how to calculate % uncertainty ?

ur stopwatch reads to the nearest 0.01 s ... so uncertainty of ur reading would be : 0.01/2 = 0.005
so %uncertainty in ur reading = (0.005/28.05)*100 = 0.02%

 

[Xtreamer]

Oh God it sure did!!
24 hrs should be over rite?

Where you guys discussing?

 

[awesomaholic101]

Where you guys discussing?

uhh no ... anyway plz temme the width was NOT 2w!!! coz i wrote 2w and changed it to √2 w

 

[Hassan Ali Abid]

View attachment 54980
2(a) (ii) number 2 for acceleration.

From marking scheme :

mg – F = ma hence a = g – [F / m]
m = ρ × V = ρ × 4/3 π R3 = (1.4 × 10–5) C1
a = 9.81 – [6.9 × 10–5] / ρ × 4/3 π × (1.5 × 10–3)3 (9.81 – 4.88) M1
a = 4.9(3) m s–2

How ? and why we got/used this equation mg – F = ma ? why why not mg + f= ma not used ? why the minus sign

weight is acting downwards,since the drop is moving down so the friction will acting in the opposite direction ie upwards , therefore
net force = W-F
ma=mg-f

where w=mg
and net force = ma.

 

[shinnyyy]

Im stuck in Hall voltage and hall probe concept and i cant find these two topics in Cambridge endorsed book so can anyone suggest me how to cover those two topics and how to understand these concepts?

 

[Xtreamer]

uhh no ... anyway plz temme the width was NOT 2w!!! coz i wrote 2w and changed it to √2 w

LOL i dont remember that one i did tukka so....do u remember the exact question? if so we can search it