Physics: Post your doubts here!

[hassankhan]

th

First of all data you are provided with
Frequency = 125 hz
tension = 4n
wavelength = 17.8/100 = 0.178m (Note : this length is given for anti node seperation, and wave length is between 2 alternative anti nodes or nodes)
therefore : 0.178 * 2 = 0.356 m (this length is of wavelength )

V= f*wavelength
v = 125 * 0.356
v = 44.5 m/s

now rooting on both sides
m = 4/44.5^2
m = 2.1 x 10^-3

thnks a lot man...

 

[gary221]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w12_qp_12.pdf

Hey guys

It's question 10 from oct/nov 2012 paper 12

Regarding the projectile motion graph, why can't it be a straight line as shown by B? Assuming there is no air resistance, the horizontal velocity has no acceleration and the vertical component has constant acceleration; therefore the graph should have straight lines instead of a curve....the answer is D and I'm not sure why.

It cant be B, as the velocity of the skier will never be constant (due to gravitational acceleration).
So, only curved lines, not straight!!

 

[gary221]

May 2011 p11 Q9 Q10 Q13
May 2011 p12 q17 2 34 37 15 10 19 32
Please solve these questions for me and explain too

s11 p12

2) You just have to remember the formula (n hence the units) of the given quantities. ie energy = force * displacement (N * m). so, a is correct.
b) power = work/ displacement (J/s) which is clearly wrong. Hence ans = b)

10) Force= mass * acceleration. Clearly the direction of the force is decided by the dir. of acceleration (which is the only vector quantity).
So, force n acceleration MUST be in the same direction.
Whereas acceleration = velocity/ displacement (both vector quantities). So, dir of acceleration may nt b d same as velocity.

 

[gary221]

15) For 2 forces to be a couple, they must b in the opp dir, perpendicular to the object----> http://www.s-cool.co.uk/a-level/physics/moments-couples-and-equilibrium/revise-it/couples
So, only B fulfils tht category. A will cause a resultant force. C= no resultant force n no couple. D = forces nt parallel, hence nt a couple.

19) Energy = Force * displacement
10 = x * 5 *10^(-3) m
So, x= 10 /(5 *10 ^-3) = 2000 N
ans = D

 

[gary221]

34) V = IR ie voltage/p.d is directly proportional to resistance, n current is inversely proportional to resistance.
So, when R increases, terminal pd will also increase.
(remember cell emf = terminal pd + lost volts due to internal resistance)
also, when R increases, current in the circuit will decrease.
Plus, emf of the cell is unchanged.
So, the ans is D, max output will be whn R = r, ----> http://www.s-cool.co.uk/a-level/phy...tential-dividers/revise-it/potential-dividers

37) B
when light falls on the LDR, its resistance decreases.
And, as we know pd is proportional to resistance, so when LDR's resistance falls, the pd across it will decrease.
And, since this is a potential divider circuit, (see abv), the pd across the resistor will increase ( voltage across R = [R/(R + LDR)] * V )

P.S. m nt sure abt 17 n 32. will gt back 2 u on tht, IA.
Hope u gt it!! All the best!!

 

[daredevil]

s11 p12

2) You just have to remember the formula (n hence the units) of the given quantities. ie energy = force * displacement (N * m). so, a is correct.
b) power = work/ displacement (J/s) which is clearly wrong. Hence ans = b)

10) Force= mass * acceleration. Clearly the direction of the force is decided by the dir. of acceleration (which is the only vector quantity).
So, force n acceleration MUST be in the same direction.
Whereas acceleration = velocity/ displacement (both vector quantities). So, dir of acceleration may nt b d same as velocity.

oh i actualy know these points/// like both of them seriously i think i looked up the wrong ms wen checking my answer >__< thanks anyways u were a great help

 

[daredevil]

15) For 2 forces to be a couple, they must b in the opp dir, perpendicular to the object----> http://www.s-cool.co.uk/a-level/physics/moments-couples-and-equilibrium/revise-it/couples
So, only B fulfils tht category. A will cause a resultant force. C= no resultant force n no couple. D = forces nt parallel, hence nt a couple.

19) Energy = Force * displacement
10 = x * 5 *10^(-3) m
So, x= 10 /(5 *10 ^-3) = 2000 N
ans = D

but in 15 they say zero resultant force ryt??

 

[daredevil]

15) For 2 forces to be a couple, they must b in the opp dir, perpendicular to the object----> http://www.s-cool.co.uk/a-level/physics/moments-couples-and-equilibrium/revise-it/couples
So, only B fulfils tht category. A will cause a resultant force. C= no resultant force n no couple. D = forces nt parallel, hence nt a couple.

19) Energy = Force * displacement
10 = x * 5 *10^(-3) m
So, x= 10 /(5 *10 ^-3) = 2000 N
ans = D

OMG i can't believe it... 19th was that simple?? O.O i was moving into another dimension
thankss sooooo much for ur help

 

[daredevil]

May 2011 p11 Q9 Q10 Q13

 

[daredevil]

34) V = IR ie voltage/p.d is directly proportional to resistance, n current is inversely proportional to resistance.
So, when R increases, terminal pd will also increase.
(remember cell emf = terminal pd + lost volts due to internal resistance)
also, when R increases, current in the circuit will decrease.
Plus, emf of the cell is unchanged.
So, the ans is D, max output will be whn R = r, ----> http://www.s-cool.co.uk/a-level/phy...tential-dividers/revise-it/potential-dividers

37) B
when light falls on the LDR, its resistance decreases.
And, as we know pd is proportional to resistance, so when LDR's resistance falls, the pd across it will decrease.
And, since this is a potential divider circuit, (see abv), the pd across the resistor will increase ( voltage across R = [R/(R + LDR)] * V )

P.S. m nt sure abt 17 n 32. will gt back 2 u on tht, IA.
Hope u gt it!! All the best!!

ummm i din't understand these two waisay -_-
can u explain 34 further?

and in 37 is it a potential divider circuit? i don't see an output voltage separatly

 

[gary221]

minie23
6 a) 92 protons in the nucleus and 92 electrons around nucleus.
[u just hv 2 know what is the atomic no.(no of protons) which is always equal to the no. of electrons in a neutral atom. Since atomic no = 92, protons=92 e=92]
143 neutrons (in the nucleus).
[the mass no = no of nucleons (ie protons + neutrons). So, no of neutrons = 235-92 = 143.

b i) α-particle travels short distance in air. hence vaccum, so tht the particle can travel a gr8r distance.
ii) very small proportion in backwards direction / large angles ----> most of mass is in very small volume (nucleus) and is charged (positive charge)
majority pass through with no /small deflections ---> most of atom is empty space.

c) α-particle is an helium atom. Atomic no = 2, so, charge = 2 * 1.6 * 10^-19 C [ 1.6 * 10^-19 is the charge on a single electron]
I = Q/t -----> t = Q/I -----> n/t = I/Q
[we just inversed the equation. bcoz in the ans the unit reqd is s–1] -----> so, n/t = (1.5 * 10^-12)/(2 * 1.6*10^-19)----> 4.7*10^6s–1

 

[PhyZac]

gary221
http://papers.xtremepapers.com/CIE/...and AS Level/Physics (9702)/9702_w06_qp_1.pdf
Question 21..

I am sure it is easy, but cant get correct answer..!

 

[gary221]

I remember tht...kinda tough, hold on.

pressure = density * g * height
pressure in the hole = 17.5MPa = 17.5 * 10^6 Pa, which is a result of the pressures of both the liquids p1 n p2
So, P(hole) = P1 + P2
17.5 * 10^6 = (d1 * g * h1) + (d2 * g * h2) ------> d1 = density of water = 1000kgm^-3 h1 = 2000 - x m
d2 = density of oil = 830 kgm^-3 h2 = x m
17.5 * 10^6 = [10000 * 9.81 * (2000-x)] + [830 * 9.81 * x]
17.5 * 10^6 = 9810 x + 19620000 + 8142.3 x
x =1271 m

 

[gary221]

^ D

 

[Izzk Ji]

GUYS URGENT HELP NEEDED WITH THIS QUESTION PAPER 2 OCT NOV 2006!!!

LINK HERE :http://papers.xtremepapers.com/CIE/...and AS Level/Physics (9702)/9702_w06_qp_2.pdf

I DIDNT UNDERSTAND WHY THE MASS IS ONLY 4 IN 3 c) ii BUT 4 X 1.66 *10^-27 IN QUESTION 3b)

THANX 4 U R SUPPORT...

 

[PhyZac]

I remember tht...kinda tough, hold on.

pressure = density * g * height
pressure in the hole = 17.5MPa = 17.5 * 10^6 Pa, which is a result of the pressures of both the liquids p1 n p2
So, P(hole) = P1 + P2
17.5 * 10^6 = (d1 * g * h1) + (d2 * g * h2) ------> d1 = density of water = 1000kgm^-3 h1 = 2000 - x m
d2 = density of oil = 830 kgm^-3 h2 = x m
17.5 * 10^6 = [10000 * 9.81 * (2000-x)] + [830 * 9.81 * x]
17.5 * 10^6 = 9810 x + 19620000 + 8142.3 x
x =1271 m

I thought it was simple ! Anyway, i think i got it, i will re review if i get doubt i will ask you. THANKS ALOOTT Jazaka Allah Khairan, May Allah S.W.T have mercy on you and your family, and grant you with the highest grades in this life and hereafter..Aameen..!! Thanks aloot!!!

 

[gary221]

GUYS URGENT HELP NEEDED WITH THIS QUESTION PAPER 2 OCT NOV 2006!!!

LINK HERE :http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w06_qp_2.pdf

I DIDNT UNDERSTAND WHY THE MASS IS ONLY 4 IN 3 c) ii BUT 4 X 1.66 *10^-27 IN QUESTION 3b)

THANX 4 U R SUPPORT...

the mass is 4u (u =unified atomic mass unit)
So, convert the mass 4u into kg ----> 4 * u (u = 1.66 * 10 ^-27 kg. given at the start of the ppr--> http://prntscr.com/11zleg
hence mass = 4 * 1.66 * 10^-27 kg.

 

[Izzk Ji]

the mass is 4u (u =unified atomic mass unit)
So, convert the mass 4u into kg ----> 4 * u (u = 1.66 * 10 ^-27 kg. given at the start of the ppr--> http://prntscr.com/11zleg
hence mass = 4 * 1.66 * 10^-27 kg.

thanks man... when we take momentum mass x velocity here , we are taking mass to be 4 and not 4u in question c ii) why??

 

[Haider2011]

I need A2 formula list and definitions

 

[Hassi123]

PHY A2 HELP!
http://www.novapapers.com/images/PDF/CIE/A-LEVEL/Physics/2012nov/9702_w12_qp_41.pdf
Q9 bi } I get that we make a square wave but how do we figure out the cross over points?