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Physics: Post your doubts here!

Thought blocker

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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
 
mahmuda akter

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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
 
Ahmed H. Al-Neel

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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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Wolfgangs said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w10_qp_12.pdf

Q11. someone please explain it.
Click to expand...
The tension in the rope needs to balance out the weight of the student acting downwards, so since the total tension needs to be opposite and equal to the weight, Let tension in rope on left side be T1 and the tension on rope on right side T2 and :. Total tension = T1sino + T2sino
add them up... W= 2Tsino, rearrange to get T= W/ 2sino. Answer: B
 
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Ahmed H. Al-Neel said:
help with question 7,33,34 and 40 plz!
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s07_qp_1.pdf
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7)
Both the other quantities are velocities. Thus X should represent the velocity due to the force F. Answer is thus C, as product of a and t would give us the velocity due to that acceleration for the specified time.
33)
V1= 5000/ (5000+5000) x 2 = 1V then V2= 3000/ (3000 + 2000) x 2 = 1.2 so V1 - V2 = -0.2 so C
34)
As Light intensity increases,Resistance decreases, R is proportional to voltage, Voltmeter reading decreases. So option A has only decrease so answer is A.
40)
We need to divide Proton numbers by their nucleon numbers, that is
for H speed would be 1 , for He it would be 1/2 ,for Li it would be 3/7 ,for Be it would be 4/9
Hence, Li has the lowest value of speed hence answer is Li
More detail :¬
u have to calculate the charge to mass ratio, whichever is the lowest will have the least acceleration.
q/m ratio of hydrogen = 1/1 = 1
q/m ratio of helium = 2/4 = 0.5
q/m ratio of lithium = 3/7 = 0.42
q/m ratio of beryllium = 4/9 = 0.44
 
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Ahmed H. Al-Neel said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s11_qp_11.pdf
question 9,25,27,37
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9)
Initial m = Final m

mv + 0 = 2mx (note: after the bodies stick, their masses combine. Let their combined speed be 'x').
mv = 2mx
x = v/2 (m cancel out)

Since the initial momentum is mv, the final momentum must be the same, so its mv also.

K.E after is given by,

0.5 * (2m) * (v/2)^2
= mv^2/4

Hence A.

25)
Use the formula (2n - 1)*75 i.e, for n = 1 we have frequency of 75Hz
we are asked for n = 2,3
n = 2 --> 3*75 = 225
n = 3 --> 5*75 = 375
Hence answer is D

27)
find d which is 1/n -->1/500 * 10^ (-3) = 2 x 10^-6.
then d sin90=n x (600 x 10^-9) = 3 then he asked for the images so it is 3 orders for one side which is 45 degrees so for the 90 degrees it is 3 x 2= 6 + the normal ray = 7 so D

37)
he want the ratio of the V1/V2 so we need the distance of R1 from x divided by the distance of R2 from x...the distance from R1 from X is x and the distance of R2 from X is the total wire length - the distace of R1 from X so it is L-x so the answer is D x/L-x
 
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