Physics: Post your doubts here!

[unique840]

Asalam-o-alaikum
please help me with these questions. Physics paper 11 may 2011 questions 14, 15, 35.
http://www.xtremepapers.com/CIE/International A And AS Level/9702 - Physics/9702_s11_qp_11.pdf

thank you very much.

35) total resistance is
1/r = 1/1 + 1/2 + 1/5
r= 0.588 ohms
total currrent is 5A
v = IR
v = 5*0.588
= 2.94
voltage is parallel does not divide
so voltage in 2ohms resistor will be 2.94 volts
v=ir
2.94 = i * 2
i = 1.5

 

[leadingguy]

Asalam-o-alaikum
please help me with these questions. Physics paper 11 may 2011 questions 14, 15, 35.
http://www.xtremepapers.com/CIE/International A And AS Level/9702 - Physics/9702_s11_qp_11.pdf

thank you very much.

we know that current entering circuit is equal to leaving the circuit according to khirchoff's law

now I =v/r thsi is the equation for current
now current in resistor of 1 ohm = I1=v/1
2 ohm = I2=v/2
5 ohm = I3 v/5 ..... remember V being same as voltage never divides in paralel circuit!

now total curren I is 5 amperes we have the eq. I1+ I2=I3 = 5

substitute values of I1 , I2 ,I3 and find the unknown voltage! which will be V = 50/17. = 2.94volts

now fr finding current in resistor of 2 ohms! V=IR I=V/R 2.94/2 = 1.47 round of to get 1.5amperes Ans.



hope u get it well???? let me know abt it???

 

[leadingguy]

Asalam-o-alaikum
please help me with these questions. Physics paper 11 may 2011 questions 14, 15, 35.
http://www.xtremepapers.com/CIE/International A And AS Level/9702 - Physics/9702_s11_qp_11.pdf

thank you very much.

sorry buddy in a rush at the moment cant tell u the ans of 14 as it needs some careful thoughts!

 

[omg]

//http://www.xtremepapers.com/CIE/International A And AS Level/9702 - Physics/9702_w07_qp_4.pdf
q.10! how do v know dat its amplitude modulated?/?

 

[smzimran]

//http://www.xtremepapers.com/CIE/International A And AS Level/9702 - Physics/9702_w07_qp_4.pdf
q.10! how do v know dat its amplitude modulated?/?

Check the frequency:
Firstly, the frequency is in kHz not MHz
Secondly, the bandwith is +-5 that is a characteristic of AM

 

[hassam]

Check the frequency:
Firstly, the frequency is in kHz not MHz
Secondly, the bandwith is +-5 that is a characteristic of AM

i quote from the book:"The frequency spectrum of a frequency-modulated
(FM) carrier wave is more complex. In particular, there
are often more than two sideband frequencies for each
signal frequency."

 

[Mustehssun Iqbal]

14) rebounding height is half of initial means potential energy is half after rebounding.
p.e = k.e therefore k.e is also half after the rebound
final k.e = 1/2 of initial k.e
1/2*m*v^2 = 1/2 (1/2*m*u^2)
v^2 = 1/2* u^2
taking square root on both sides
v = u/sqr rt of 2
v/u = (u/sqr rt of 2) / u
u cancels out
ratio is 1/sqr rt of 2

Asalam-o-alaikum
please help me with these questions. Physics paper 11 may 2011 questions 14, 15, 35.
http://www.xtremepapers.com/CIE/International A And AS Level/9702 - Physics/9702_s11_qp_11.pdf

thank you very much.

Another solution to Q.14:
you take the motion of the sphere in two parts. In the first part;
v^2 = u^2 +2as
v^2 = (0)^2 + 2(10)s
The ball is released from rest and u =0;
v^2 = 20s
s = v^2/20
the final velocity of this motion is the initial velocity of the second motion.v is replaced by u.
s = u^2/20
In the second part of the motion;
v^2 = u^2+2as
v^2 = u^2+2(-10)(s/2) - the height of the sphere in the second part of the motion is half to that in the first part of the motion.
v^2 = u^2 -10s
v^2 = u^2-10(u^2/20)
v^2 = u^2-u^2/2
v^2 = u^2/2
square root of v^2 = square root of (u^2/2)
v = u/square root of 2
v/u = u/square root of 2/u
v/u = 1/square root of 2
although Unique240 's solution to this question is faster!

 

[omg]

i quote from the book:"The frequency spectrum of a frequency-modulated
(FM) carrier wave is more complex. In particular, there
are often more than two sideband frequencies for each
signal frequency."

so it means that the frequency of FM is in Mhz?? and wht abt the bandwidth??

 

[omg]

Check the frequency:
Firstly, the frequency is in kHz not MHz
Secondly, the bandwith is +-5 that is a characteristic of AM

so it means that the frequency of FM is in Mhz?? and wht abt the bandwidth??

 

[smzimran]

so it means that the frequency of FM is in Mhz?? and wht abt the bandwidth??

Yes it is in MHz, the FM channels u listen to are FM 101 MHz, FM 107 MHz etc...
the bandwidth i do not remember exactly; check it from the booklet...

 

[hassam]

AND we DO Not have the picture for spectrum of FM in any of our books.....

 

[Anonymous']

Assalamualaikum, and hey guys! hmm.. I need help on question 3 (b) november 2001 -------> http://www.xtremepapers.com/CIE/International A And AS Level/9702 - Physics/9702_w01_qp_2.pdf

 

[DragonCub]

Assalamualaikum, and hey guys! hmm.. I need help on question 3 (b) november 2001 -------> http://www.xtremepapers.com/CIE/International A And AS Level/9702 - Physics/9702_w01_qp_2.pdf

Via intuition you can deduce that the extension in S3 is also x.
The springs are identical, so their constant of elasticity can all be seen as k.
Force on S1 (call it F1) is kx, so is force on S2 (call it F2).
The resultant force of F1 and F2 is to the left, since their vertical components cancel out each other.
Horizontal resultant force = F1 cos60 + F2 cos60 = kx/2 + kx/2 = kx
Due to equilibrium, this is the force on S3. Extension of S3 = kx/k = x

 

[Anonymous']

Via intuition you can deduce that the extension in S3 is also x.
The springs are identical, so their constant of elasticity can all be seen as k.
Force on S1 (call it F1) is kx, so is force on S2 (call it F2).
The resultant force of F1 and F2 is to the left, since their vertical components cancel out each other.
Horizontal resultant force = F1 cos60 + F2 cos60 = kx/2 + kx/2 = kx
Due to equilibrium, this is the force on S3. Extension of S3 = kx/k = x

hmm.. I don't really get this -------> Horizontal resultant force = F1 cos60 + F2 cos60 = kx/2 + kx/2 = kx
Due to equilibrium, this is the force on S3. Extension of S3 = kx/k = x

can you explain why did you put: kx/2 + kx/2 = kx and why is it: Extension of S3 = kx/k = x ?

 

[Anonymous']

Via intuition you can deduce that the extension in S3 is also x.
The springs are identical, so their constant of elasticity can all be seen as k.
Force on S1 (call it F1) is kx, so is force on S2 (call it F2).
The resultant force of F1 and F2 is to the left, since their vertical components cancel out each other.
Horizontal resultant force = F1 cos60 + F2 cos60 = kx/2 + kx/2 = kx
Due to equilibrium, this is the force on S3. Extension of S3 = kx/k = x

Wait, I think I already figured it out! heheh.. Thank you for your explanations! heheh..

 

[tom ed]

can someone plz tell me why was the average of current taken to calculate the amount of charge flowing....in (question no 30..paper 1 june 2003).the question is:.
30 The current in a component is reduced uniformly from 100 mA to 20 mA over a period of 8.0 s.
What is the charge that flows during this time?
A 160mC B 320mC C 480mC D 640mC

the answer is C

 

[DragonCub]

can someone plz tell me why was the average of current taken to calculate the amount of charge flowing....in (question no 30..paper 1 june 2003).the question is:.
30 The current in a component is reduced uniformly from 100 mA to 20 mA over a period of 8.0 s.
What is the charge that flows during this time?
A 160mC B 320mC C 480mC D 640mC

the answer is C

You can assimilate this with linear motion
charge = current × time
displacement = velocity × time
You must be familiar with calculation involving acceleration, aren't you?
It is quite similar for charge. Here the "initial current" 100 mA, "final" 20 mA, "current acceleration" is constant (uniform).
So charge (displacement) = [initial current (velocity) + final current (velocity) ]/2 × time
= (100 mA + 20 mA)/2 × 8.0 s = 480 mC

 

[tom ed]

You can assimilate this with linear motion
charge = current × time
displacement = velocity × time
You must be familiar with calculation involving acceleration, aren't you?
It is quite similar for charge. Here the "initial current" 100 mA, "final" 20 mA, "current acceleration" is constant (uniform).
So charge (displacement) = [initial current (velocity) + final current (velocity) ]/2 × time
= (100 mA + 20 mA)/2 × 8.0 s = 480 mC[/quote

yeah rite.....yes i am........thanku very much.......for telling....u have certainly mastered ths part...XD

 

[MEGUSTA_xD]

An electric railway locomotive has a maximum mechanical output power of 4.0 MW. Electrical power is delivered at 25 kV from overhead wires. The overall efficiency of the locomotive in converting electrical power to mechanical power is 80 %.
What is the current from the overhead wires when the locomotive is operating at its maximum power?
A 130A B 160A C 200A D 250A



Answer: C

 

[unique840]

output power given is 4MW. efficiency is 80%.
efficiency = output power/input power
input power = output / efficiency
input = 4MW/80%
input = 5MW
P=VI
5MW/25kV = I
I= 200A