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Physics: Post your doubts here!

Thought blocker

Thought blocker

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Ahmed H. Al-Neel said:
question 38 for : http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w13_qp_12.pdf
question 35 for : http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s13_qp_11.pdf
Click to expand...
Wait lemme see your questions :)
I solved that paper for you :
Thought blocker said:
w12_12
29)
View attachment 44719
As you can see from the figure, there will be total difference b/w nodes = 3λ / 2 = L
Now we know the velocity, we can calculate λ so f = v / λ
λ = 0.2 m
f = 1650 Hz

34)
Let's go choice by choice shall we...:
B: It's said both are made from same material. So resistivity is same.
Reject B

A:
R = (resistivity * L)/A
Both are same material so we ignore resistivity for now.
So we have: R = L/A
We have to compare their cross-section areas.
A = L/R

For X:
When R = 20, L = 0.6
A = .6/20 = 0.03A

For Y:
When R = 10,
L = 0.6,
A = 0.6/10 = 0.06A

Compare 'em.
2X = Y
Is this what dear (NOT!) A is suggesting?
No. It says the opposite in fact.
So A's a no-no.

C.
Take both lengths equal. I took them 0.6m
For X, R = 20
For Y, R = 10

P = VI
SInce they're in series, I will be same for both.

For X,
P = 20I
For Y,
P = 10I

Compare 'em away.
Power of Y *2 = Power of X
WHich is exactly what C says.
So C's our choice.

But to be clear, let
s have a look at D

In parallel, current in one of the two branches, in equal to ratio of R/total of OTHER branch.

For X, (R=20) and R = 10 for Y. Total = 30
For current in X, therefore, it's 10/30 ie 1/3 I

For Y,
20/30 I
or 2/3 I

This is clearly NOT what's in D.
So D goes down.

36)
Here first we'll find the power at two points of current provided, and as its not a fixed current we would take the mean of power we get.
So it follows as :¬
Power at 2 ampere = 4 * 100 = 400W
Power at -1 ampere = -1 * 100 = -100W
Now as I said take mean of these powers : 500 / 2 = 250W

37)
Its not D as no current will pass if both switch are open. Then its not even A as both are closed so current will be I. In B S2 is open and S1 is closed so current just flows in series so current is still I. In C current flows through parallel circuit as S1 is open and S2 closed and current is not equal in parallel so it will not be I

38)
remember when two resistor are in series, more voltage drop is at resistor with more value, so their a flashing light then R = 5 mega ohm when dark, then 5M is very large than 1 K of other resistor, then almost all voltage drop at 5M, hope you get this, it is a very simple concept.

39)
Whats the big deal here ?
You know that nucleon number in helium is 4 (helium = alpha particle)
Then from original substance 100 alpha get removed every second, so in alpha, 4 * 100 = 400 nucleon each second.

s12_12
7)
Its A, because according to velocity time graph, we can see that its negative after half the time. That means that guy has changed his direction. this describes The scenario that a man run stratis gradually increasing hi speed and then after certain reducing speed and an he changes is direction(moves backward) with same speed pattern.
Now considering this troy with displacement, that guy reaches the farthest point and then comes back i.e max displacement after halftime.

10)
Keep this thing in mind when you are asked for projectile thingy :
  • horizontal component of velocity = constant
  • vertical component of acceleration constant = constant
  • At top most, vertical velocity is zero
Now look it practically,
you throw a ball, when it reaches max height (top) it stops for a while
KE cannot be zero
KE = 0.5mv^2
v = root(square(vx) + square(vy))
vy = 0
but vx = constant
so v is nonzeror and hence KE canot be zero
similarly momentum canot be zero
P=mv :)

17)
Base has h = 0, i.e is block 1 = zero * mgh
Now we have other 3 blocks.
block 2 = at height h so m*g*h = mgh
block 3 = at height 2h = 2mgh
block 4 = height 3h = 3mgh
Sum all this P.E = 6mgh

28)
View attachment 44722

30)
Given
λ/2=33cm
so λ is 66cm or 0.66m
f=330/0.66=500
T=1/500=2ms
so it means wave should be completed in 4 blockss as the time base is 0.50ms/cm
the only one is B
Click to expand...
 
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Ahmed H. Al-Neel said:
question 38 for : http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w13_qp_12.pdf
question 35 for : http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s13_qp_11.pdf
Click to expand...
Well weren't they easy :p (jk)
38)
Here we are asked to find total EMF in the circuit.
We'll use the formula : EMF*(R1/R1+R2+R3) = V
Now we wont consider 4R coz its parallel attached to other 3 resistors, hence --> EMF*(2/6) =2 so EMF = 6V

35)
Will have to type alot, wait.
 
papajohn

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Hijab said:
I tried to.... But i could not get the correct answer... I will try it again
Click to expand...
Use the equation of motion s = ut + 0.5at^2
Now substitute the data into the equation
For XY
S= 40
t=12
u=??
a=??

equation 1 : 40 = 12u + 72a

For the X to Z
S= 80
t= 18
a=??
u=???
equation 2 : 80 = 18u + 162a
Why not I use the distance Y to Z is that it unitial velocity is different from that of X to Y
Now use simultaneus equation to get the answer..
 
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Batguy said:
physics p1 main i need some help :'|
paper oct 12 var:12 question:14,16,20 :'(​
Click to expand...
Saad ro mat :p
14)
FIRST OF ALL,BOTH NEWTON METERS ARE SHOWING TENSION IN THE STRINGS AND WE HAVE TO FIND THE VERTICAL COMPONENTS OF BOTH THE FORCES.

VERTICAL COMPONENT OF 4 NEWTONS FORCE IS: COS(37) = X/4 , SO X = 4COS(37) = 3.19N
VERTICAL COMPONENT OF 3 NEWTONS FORCE IS: COS(53) = X/3 , SO X = 3COS(53) = 1.80N

NOW WE NEED TO FIND THE RESULTANT FORCE: FORWARD FORCE(WEIGHT) - BACKWARD FORCE
12-(3.19+1.80) = 7N
NOW USE F=MA TO FIND ACCELERATION

7=1.2 x A

A = 7/1.2
A = 5.83 ms^-2 = 6 ms^-2

16)
there are three forces acting on an object as it is lowered in an liquid. gravitational pull(downwards) upthrust(upwards) and viscous drag(upwards)
upthrust is the difference between the (pressure acting on the top of object)- (pressure acing on the bottom)
Viscous drag is the force that a solid experiences as it is lowered down the object due to its viscosity or density( we rather like to say viscosity when referred to a liquid).
since the object is stationary so no viscous drag. gravitional pull equals upthrust.

20)
Use 0.5 * m * v^2 here : 0.5 * (1200 * 1000) * 75^2 = D
 
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Thought blocker said:
Saad ro mat :p
14)
FIRST OF ALL,BOTH NEWTON METERS ARE SHOWING TENSION IN THE STRINGS AND WE HAVE TO FIND THE VERTICAL COMPONENTS OF BOTH THE FORCES.

VERTICAL COMPONENT OF 4 NEWTONS FORCE IS: COS(37) = X/4 , SO X = 4COS(37) = 3.19N
VERTICAL COMPONENT OF 3 NEWTONS FORCE IS: COS(53) = X/3 , SO X = 3COS(53) = 1.80N

NOW WE NEED TO FIND THE RESULTANT FORCE: FORWARD FORCE(WEIGHT) - BACKWARD FORCE
12-(3.19+1.80) = 7N
NOW USE F=MA TO FIND ACCELERATION

7=1.2 x A

A = 7/1.2
A = 5.83 ms^-2 = 6 ms^-2

16)
there are three forces acting on an object as it is lowered in an liquid. gravitational pull(downwards) upthrust(upwards) and viscous drag(upwards)
upthrust is the difference between the (pressure acting on the top of object)- (pressure acing on the bottom)
Viscous drag is the force that a solid experiences as it is lowered down the object due to its viscosity or density( we rather like to say viscosity when referred to a liquid).
since the object is stationary so no viscous drag. gravitional pull equals upthrust.

20)
Use 0.5 * m * v^2 here : 0.5 * (1200 * 1000) * 75^2 = D
Click to expand...
thank you bro :)
 
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