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Physics: Post your doubts here!

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not.maria said:
Please can anyone explain:
q8 and q 21
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w10_qp_12.pdf

And also can anyone kindly help me out in this?
Click to expand...
8)
lets see the motion in XY
initial velocity at x=v1
final velocity at y=v2
average velocity=distance/time
(V1+V2)/2=40/12 equation 1
simplifying it we get V1+V2=6.67

now consider motion in XZ
initial velocity at x=v1
final velocity=v3
V1+V2/2=(40+40)/(12+6)
simplifying it we get V1+V3=8.89 equation 2
subtract equation 1 from 2
i mean equation 2-equation 1
V1 is cancelled and we get V3-V2=2.22
since acceleration is constant so
acceleration in yz = acceleration in xz
= change in velocity/time
=2.22/6
=0.37

21)
Oh,
For these type of questions...i strongly suggest u to assume numerical values yourself..according to question..like if it says P has diameter twice than that of Q..than assume diameter of q=2cm...and therefore P=4cm..these assumptions will make it easy for u, if you still have a doubt, don't hesitate to ask.

18)
There are range of speeds of moelcules.
Some move with slow speed and some move with high speed.
Only some molecules which have higher kinetic energy will move an escape liquid.
And we dont say that solid and liquid have molecular potential enrgy as attractive forces
Hence it is C :)

19)
sugar is a polymer of monossacrides (glucose) and nylon is a condensation polymer so C

20)
total pressure = pressure at surface + pressure due to liquid
so P = ρgh --> 1030 * 9.8 * 80 = 807520
Now add it to 100000 that equals approx of 900000 hence D :)
 
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Thought blocker said:
8)
lets see the motion in XY
initial velocity at x=v1
final velocity at y=v2
average velocity=distance/time
(V1+V2)/2=40/12 equation 1
simplifying it we get V1+V2=6.67

now consider motion in XZ
initial velocity at x=v1
final velocity=v3
V1+V2/2=(40+40)/(12+6)
simplifying it we get V1+V3=8.89 equation 2
subtract equation 1 from 2
i mean equation 2-equation 1
V1 is cancelled and we get V3-V2=2.22
since acceleration is constant so
acceleration in yz = acceleration in xz
= change in velocity/time
=2.22/6
=0.37

21)
Oh,
For these type of questions...i strongly suggest u to assume numerical values yourself..according to question..like if it says P has diameter twice than that of Q..than assume diameter of q=2cm...and therefore P=4cm..these assumptions will make it easy for u, if you still have a doubt, don't hesitate to ask.

18)
There are range of speeds of moelcules.
Some move with slow speed and some move with high speed.
Only some molecules which have higher kinetic energy will move an escape liquid.
And we dont say that solid and liquid have molecular potential enrgy as attractive forces
Hence it is C :)

19)
sugar is a polymer of monossacrides (glucose) and nylon is a condensation polymer so C

20)
total pressure = pressure at surface + pressure due to liquid
so P = ρgh --> 1030 * 9.8 * 80 = 807520
Now add it to 100000 that equals approx of 900000 hence D :)
Click to expand...
Thanks alot! this is helping me soo much:)

however q18 19 20 were for this paper:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w10_qp_12.pdf
:)
 
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_Ahmad said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w07_qp_1.pdf

Q11,23,25,27,40 PLEASE HELP
Click to expand...
11)
Attached at the end.

23)
We are provided with V = 8 m/s, Max speed = 2πaf, mass = 2 * 10 ^ (-3)
Maximum K.E = 0.5 * m * (max speed)^2
Max speed = 2 * π * 2 * 8/50 -- > We got a from graph, and f from graph itself. a = 2 and f = v / lambda = 8 / 50 (50 from graph)
so K.E = 4 mJ

25)
d sin theta = n lambda
d sin 45 = 3 lambda
d o.7 = 3 lambda
now we are asked to find highest order grating, it means highest value of sin theta, and we know sin 90 has higest value of 1
now we got other equation
d = n lambda
now divide 1 from 2
0.7 = 3 / n
n = 4

27)
D, basic concept yaar.

40)
P = vm
it means p is proportional to m
so alpha has highest mass of 4 so A is the answer

I am in hurry, so gave overview, if you have doubts, surely ask 'em :)
 

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immie.rose said:
Please help!
View attachment 44359
Answer : D
Click to expand...

Since both wires are made of steel, they have the same Young's Modulus value (which is a measure of how easy it is to stretch or compress the material, and is a property of the material itself, not a sample - so, any two pieces of the same material will have the same Young's Modulus).

The formula for Young's Modulus is given by

Y = Fl/Ax = Fl/Ae

Where Y = Young's Modulus,
F = Magnitude of Force stretching or compressing the sample,
l = Length of Sample when no force is applied on it,
A = Cross Sectional Area perpendicular to the Force and the length of the sample, and
x = e = change in length of the sample in the direction of the stretching/compressing force.

So, we know that the extension is the same for both wires (that is what they have given in the question) and the Young's Modulus is the same for both wires - this means that the product eY (or xY) is the same for both samples. Rearranging the formula, we get

eY = xY = Fl/A

So the product Fl/A is the same for both wires.

Let's take P. We don't know what the stretching force is, so we'll simply write it as F(p). We know the length of P is l and that the cross sectional area is A. Therefore, we can write the product as

Fl/A = F(p)l/A

Now let's move on to wire Q. Again, we don't know what the stretching force is, so let's call it F(q). The length of Q is 2l and the cross sectional area is A/2. So, we can write the product as

Fl/A = F(q) * (2l)/(A/2) = 4F(q)l/A

Equating these, we get

F(p)l/A = 4F(q)l/A

Multiplying both sides by A and dividing by l, we get

F(p) = 4F(q)

So that F(p)/F(q) = 4 = 4/1

One last thing we can say is that the tension in the wire is equal to the force stretching the wire (by Newton's Third Law, I guess - i'm not too sure about this part, but suppose you pulling the wire at one end - your muscles are pulling your fingers, and the tension in the rope is pulling them in the opposite direction. The stretching force, in that case, as long as the wire is stationary, must be equal to the tension force. That's my reasoning here, but i'm not too sure about it).

Therefore, F(p)/F(q) = (Tension in P)/(Tension in Q) = 4/1 = D.

Hope this helped!
Good Luck for all your exams!
 
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mahmuda akter said:
help plz
may-june 2011/12
question 17
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s11_qp_11.pdf
Click to expand...
Thought blocker said:
You posted link of 2011/11
Make sure, what is your correct doubt :)
Click to expand...

Well, gtg here is both answers...
9702_s11_qp_12
17)
Perpendicular =80/2 =40 mm

Find the angle.
Sin Θ = 40/50= 53.1°

As there are two tensions both equal, so Force = 2(cos 53.1 x 4) = 4.8 N

9702_s11_qp_11
17)
From 1st info, calculate the mass - m = K.E / 0.5*V^(2) = 30 kg
Now from second info find out K.E using the same mass.
K.E = 0.5*30*40^(2) = 24000 J
 
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Thought blocker said:
Well, gtg here is both answers...
9702_s11_qp_12
17)
Perpendicular =80/2 =40 mm

Find the angle.
Sin Θ = 40/50= 53.1°

As there are two tensions both equal, so Force = 2(cos 53.1 x 4) = 4.8 N

9702_s11_qp_11
17)
From 1st info, calculate the mass - m = K.E / 0.5*V^(2) = 30 kg
Now from second info find out K.E using the same mass.
K.E = 0.5*30*40^(2) = 24000 J
Click to expand...


oopss sry.. its the one from variant 12... & thankss for the solution.:)
 
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Ahmed H. Al-Neel said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s10_qp_11.pdf
help with question 4,16,22,29,33 please
Click to expand...
4)
10 ms = 1cm , total 8.5 waves in 6 cm, so if 10 ms = 1 cm so 6 cm = 60 ms and 60 ms = 0.006 s
So in 0.06 s there are 8.5 waves. so in 1 wave what is the value of time, that will be 0.00706 s
As you know f = 1 / T, f = 1 / 0.00706 = 141 that is 140 approx so B

16)
The Efficiency = (Useful Output energy)/(Total Input Energy).
•Since the kinetic energy of the car doesn't change and remains at v, there is no change in the kinetic energy of the car.
•Since friction does not do any work (we can assume this, and even otherwise it is not useful output so it doesn't count) there is no energy lost to internal energy.
•However, potential energy does change - the car moves up a height of mgs * sin(α) (Since ΔP.E. = mgΔh, and sin(α) = Δh/s, Δh = s * sin(α) and ΔP.E. = mgs * sin(α)).
•Therefore, the useful energy output = mgs * sin(α)
•The work we put into the system is the only input to the system; no other influence is exerted by us, so the only input to the system is the work done by our force = F.
This work = F.s = Fs.

So, (Useful Output Energy)/(Total Input Energy) = mgs * sin(α)/Fs = mgsin(α)/F
Hence your answer is D

22)
Infra - red waves wary from 10^-4 to 10^ -7 so answer is C

29)
electron will always move in direction parallel to the direction of the beam. electron repel electron so it would move in opposite direction
so D.

33)
There are lots of ways for this question
I find V the easiest to use in an explanation
PQR all have same resistance
Q,R have same V while P has 2x of their V so 2V
Power = (V^2)/R
so Power ratio of P Q R =((2v)^2)/R: (V^2)/R : (V^R)/R or 4:1:1
total power is 12, divided to 6 parts so Power of R is 2W
 
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Thought blocker said:
4)
10 ms = 1cm , total 8.5 waves in 6 cm, so if 10 ms = 1 cm so 6 cm = 60 ms and 60 ms = 0.006 s
So in 0.06 s there are 8.5 waves. so in 1 wave what is the value of time, that will be 0.00706 s
As you know f = 1 / T, f = 1 / 0.00706 = 141 that is 140 approx so B

16)
The Efficiency = (Useful Output energy)/(Total Input Energy).
•Since the kinetic energy of the car doesn't change and remains at v, there is no change in the kinetic energy of the car.
•Since friction does not do any work (we can assume this, and even otherwise it is not useful output so it doesn't count) there is no energy lost to internal energy.
•However, potential energy does change - the car moves up a height of mgs * sin(α) (Since ΔP.E. = mgΔh, and sin(α) = Δh/s, Δh = s * sin(α) and ΔP.E. = mgs * sin(α)).
•Therefore, the useful energy output = mgs * sin(α)
•The work we put into the system is the only input to the system; no other influence is exerted by us, so the only input to the system is the work done by our force = F.
This work = F.s = Fs.

So, (Useful Output Energy)/(Total Input Energy) = mgs * sin(α)/Fs = mgsin(α)/F
Hence your answer is D

22)
Infra - red waves wary from 10^-4 to 10^ -7 so answer is C

29)
electron will always move in direction parallel to the direction of the beam. electron repel electron so it would move in opposite direction
so D.

33)
There are lots of ways for this question
I find V the easiest to use in an explanation
PQR all have same resistance
Q,R have same V while P has 2x of their V so 2V
Power = (V^2)/R
so Power ratio of P Q R =((2v)^2)/R: (V^2)/R : (V^R)/R or 4:1:1
total power is 12, divided to 6 parts so Power of R is 2W
Click to expand...
i am still speechless the least thing i can do is thank you, i will pray for u during each prayer inshallah u will always succeed in life.
 
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