Physics: Post your doubts here!

[white rose]

what hes saying is:
s=ut + 0.5at^2

so taking s=40 and t=12

40=12u + 0.5(a)(12)^2
40=12u + 0.5(a)(144)
40=12u + 72a

thank u Maira...

 

[Aymen Ezazi]

View attachment 28828
Can anybody tell me how to do ds question

is the answer B??

 

[Adorkableme]

can someone please help me with Q 12,19,27,30,36 from Winter 2012 ...... http://papers.xtremepapers.com/CIE/...nd AS Level/Physics (9702)/9702_w12_qp_12.pdf

 

[Sohail A. Razzak]

is the answer B??

Yes it is

 

[Adorkableme]

can someone please help me with Q 12,19,27,30,36 from Winter 2012 ...... http://papers.xtremepapers.com/CIE/...nd AS Level/Physics (9702)/9702_w12_qp_12.pdf

 

[1597.2217]

Q4, 5, 15
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w11_qp_11.pdf

Q4-

LHS = RHS
The units must be cancelled out so that nothing remains. First, you cancel out all the constants:
L x 1/P = Q x T^2 [We know L is m and T is s]
m x 1/P = Q x s^2 [To cancel the s^2, Q must have s^-2]
Now substitute the units given in options:
(B) m x m^-2 = m x s^-2 x s
Giving m = m

Q5-

Basically what they are asking is to first find the PERCENTAGE UNCERTAINTY. Eg, for A- 0.002/2.043 x 100% gives 0.097%.
Find out for other options. You will see that B- has 3.7% and D- has 3.85%. But it doesn't end here. (B) is d, and in the equation the d is multiplied by d again. So multiply the uncertainty giving you value greater than (D).

Q15-

Total AC moment = Total C moment.
The rings are of same mass.
7xm + Yxm = 5x2m [Subs m as 1 for simplicity]
7 + y = 10
y = 3
[8 from pivot minus 3 = 5.]
Ans is hence (C)


Good luck tomorrow. Remember me in yours prayers please.

 

[killer22]

Y is da answer not c but d???
View attachment 28829

Long explanation. Just memorise the answer.

 

[1597.2217]

can someone please help me with Q 12,19,27,30,36 from Winter 2012 ...... http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w12_qp_12.pdf

Q12-
Remember the equation: F=Change in momentum/time
Change in momentum:
0.5x12 = o.5x-8
Change is 10
10/0.1 = 100
So (D)

Q19-
P = F/A
F = P x A
F = 4000 x 500/100x100 [Convert cm^2 to m^2]

Wd = F x s
200 x 0.3 = 60

Ans is (A)

Q27-
Y = FxL/AxX
L and X are constant for both.
(Y) of X = 1/2 (Y) of Y
So F/x = F/2x [Don't include L and A because they are same for both.]
You see that the ratio is 1:2 so (B)

Q30-
Sorry no idea, don't have Sin O here.
Otherwise 1/300x10^-3 x Sin O = n x 690x10^-9

Q36-
P = I^2 x R
Max = 400
Min = 100
There are 5 max and 4 min, so
5 x 400 + 4 x 100 / 9
= 266.6

Comes close to (C) of 250


Good luck tomorrow. Please remember me in yours prayers.

 

[1597.2217]

Y is da answer not c but d???
View attachment 28829

Because (t2-t1)^2 is the square of the time difference.
However, t2^2 - t1^2 will you you difference of squares of both answers, which not the same value as above.

Lets take T1 as 3 and T2 as 5.
(5-3)^2 = 4.000
5^2 - 3^2 = 16.000

 

[Lyfroker]

Q4-

LHS = RHS
The units must be cancelled out so that nothing remains. First, you cancel out all the constants:
L x 1/P = Q x T^2 [We know L is m and T is s]
m x 1/P = Q x s^2 [To cancel the s^2, Q must have s^-2]
Now substitute the units given in options:
(B) m x m^-2 = m x s^-2 x s
Giving m = m

Q5-

Basically what they are asking is to first find the PERCENTAGE UNCERTAINTY. Eg, for A- 0.002/2.043 x 100% gives 0.097%.
Find out for other options. You will see that B- has 3.7% and D- has 3.85%. But it doesn't end here. (B) is d, and in the equation the d is multiplied by d again. So multiply the uncertainty giving you value greater than (D).

Q15-

Total AC moment = Total C moment.
The rings are of same mass.
7xm + Yxm = 5x2m [Subs m as 1 for simplicity]
7 + y = 10
y = 3
[8 from pivot minus 3 = 5.]
Ans is hence (C)


Good luck tomorrow. Remember me in yours prayers please.

Thnx a lot n same to u

 

[Lyfroker]

Q#9, 11, 18, 24 & 37
http://papers.xtremepapers.com/CIE/...nd AS Level/Physics (9702)/9702_w10_qp_11.pdf

 

[6Astarstudent]

Q#9, 11, 18, 24 & 37
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w10_qp_11.pdf

#9: V^2=U^2 + 2 as
so original equation 0 = U^2 + 2ax
increase in initial velocity by 20% so 0 = (1.2U)^2 + 2ax = 1.44U^2 + 2ax
X is proportional to U so answer is C, 1.44x

#18 solved by Gain in potential energy of m1 minus loss in potential energy in m2. the change in energy is the work done by the motor.
so Ep=mgh and change in Ep = m1gh - m2gh = (m1-m2)gh.
question is asking for power (rate of change of work) so divide the work done by time. (m1-m2)gh/t = (m1-m2)gv ansewr is D

#24 since it is a progression wave, picture another wave less than or equal to π/2 infront of it (direction of wave). notice only B and D is moving up. and then the velocity is the gradient of the wave so greater gradient at B so answer it B.

#37
The Voltmeter is parallel to both resistors, not just one. so there is no change in pd so answer is A

 

[Zaibyraja]

Could someone please help me with may/June/12/2012 pleasee.
Mcq no 13,18 and 24.
Here's a link to the paper: http://papers.xtremepapers.com/CIE/...nd AS Level/Physics (9702)/9702_s12_qp_12.pdf

 

[6Astarstudent]

Could someone please help me with may/June/12/2012 pleasee.
Mcq no 13,18 and 24.
Here's a link to the paper: http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s12_qp_12.pdf

#13
F(net force) = ma
F(net) = 2x9.81(the weight) - 6(friction) = 13.62
total mass = 8+2 = 10
F=ma
A=F/M = 13.62/10 = 1.4 so answer is A

#18
efficiency = output power/input power
in this case its a generator so output power is P=VI = 230 x 32=7360
input power = E(potential) / time = Mgh/t = 200 x 8 x 9.81 = 15696
efficency = 7360/15696 x 100%=47% answer is D

#24
simply find the area inclosed by the graph and x = 0 to x= 7mm

 

[Zaibyraja]

#13
F(net force) = ma
F(net) = 2x9.81(the weight) - 6(friction) = 13.62
total mass = 8+2 = 10
F=ma
A=F/M = 13.62/10 = 1.4 so answer is A

#18
efficiency = output power/input power
in this case its a generator so output power is P=VI = 230 x 32=7360
input power = E(potential) / time = Mgh/t = 200 x 8 x 9.81 = 15696
efficency = 7360/15696 x 100%=47% answer is D

#24
simply find the area inclosed by the graph and x = 0 to x= 7mm

Thankyou so much. On the last mcq however the answer I get is A whereas the mark scheme says B :/ and if someone could do 17 as well I'd really apprciate that. The answer to that is B

 

[6Astarstudent]

Thankyou so much. On the last mcq however the answer I get is A whereas the mark scheme says B :/

wierd, I just did calculation again and it is B.
You can always use the last resort by counting the squares. I counted 243 squares and each area of square is 5x10^-4 so I get 0.1215 J which is B

 

[hope4thebest]

Ans is A. Can someone explain?

 

[Oceanic]

View attachment 28827

Both questions please!
Answers are
17: A
18: B

17 is a because only that body cannot stay in that position ie it will move down the slope.
No clue about 18 though
But which app is this ?

 

[Tkp]

17 is a because only that body cannot stay in that position ie it will move down the slope.
No clue about 18 though
But which app is this ?

for no. 18
v2=u2-2gs
v2=28^2-2*9.81*22=19
so ans is B

 

[Kyusam]

http://papers.xtremepapers.com/CIE/...nd AS Level/Physics (9702)/9702_s12_qp_12.pdf
Ok so I'm done with every single thing except this question which is literally haunting me :'( plzzz plzzzz plzzzz if some1 knows it answers it pleaseeeeee it's Q:30