Physics: Post your doubts here!

[aniroula]

Can some one help.me please,,

May/june 2009 q no 4 b spring constant arrangement.. I knew how to find extension but not spring constant,,

 

[aniroula]

You should know that a spring constant ‘k’ is a measure of how stiff the spring is. A spring that is very hard to stretch out has a large spring constant. A spring that is easy to stretch has a small spring constant. As the term spring constant implies, the spring constant is always the same for a given spring. It is the force applied per unit extension or there is another way, take this as Electricity (Springs in series and Springs in Parallel) which come's under my category of "Desi Totka's"
Now, here in this question. at first the extension is double (2E) as springs are in series and spring constant is half (1/2K).
In the second part, extension is halved(1/2E) as springs are in parallel and spring constant is doubled(2K).
And the last one, focus on the parallel series first and then the single spring. For extension parallel + single = 3/2E and for Spring constant parallel + single = 2/3K

Could you plz explain the last part,,, for spring constant

 

[emkay]

Could you plz explain the last part,,, for spring constant

for the last part, consider the stretching of parallel springs by that single spring (it would be hard compared to the previous springs). Recall the definition that i previously wrote about spring constant and then relate that with this condition. it's pretty easy, a single spring takes a lot of effort in stretching the parallel springs. when springs are in parallel, spring constant is added Ktotal = (K1+K2)k so 2/3K.
arrangement value of k / K
single spring = 1
two springs in series = ½
three springs in series = ⅓
two springs in parallel = 2
three springs in parallel = 3

 

[aniroula]

for the last part, consider the stretching of parallel springs by that single spring (it would be hard compared to the previous springs). Recall the definition that i previously wrote about spring constant and then relate that with this condition. it's pretty easy, a single spring takes a lot of effort in stretching the parallel springs. when springs are in parallel, spring constant is added Ktotal = (K1+K2)k so 2/3K.
arrangement value of k / K
single spring = 1
two springs in series = ½
three springs in series = ⅓
two springs in parallel = 2
three springs in parallel = 3

Thanks bro..,,

 

[aniroula]

Plz help with this..
May,june 11 paper 23 qno 3 d i and ii
Qno 4c ii and iii and 5 i

 

[aiskw1]

Plz help with this..
May,june 11 paper 23 qno 3 d i and ii
Qno 4c ii and iii and 5 i

For 5i) the filament lamps resistance increases due to the increasing current. As current passes through (the electrons or whatever not sure, collide with the particles or atoms of the stuff in the resistor and release heat energy... colliding is resistance I think) therefore heat energy being released increases the temperature of the lamp which causes the atoms in the lamp to vibrate to a higher degree [not sure if amplitude can be used in this sentence but I will use this anyway], so the electrons collide more with the atoms, and the resistance increases.

Therefore in summary:

If current increases
Temperature increases with greater current
Resistance increases with greater temperature
Voltage decreases

therefore on the graph as I increases V decreases

 

[aiskw1]

Okay it's just vibrations getting faster and further

I think this explains everything for question 5

source: http://www.passmyexams.co.uk/GCSE/physics/images/Potential_Difference_graph_Filament_Lamp.jpg

 

[Silent Hunter]

In the projectile motion?
when the ball is thrown upwards and it just touches the height of the wall.... will we take acceleration as -9.81 ? or +9.81 ?

like in this paper: http://www.xtremepapers.com/papers/...nd AS Level/Physics (9702)/9702_w10_qp_22.pdf question 2 (a)(ii) they have taken s = ut - 0.5at^2 why "-" ? why not plus?

 

[queen of the legend]

My doubt is related to the question I attached.

How currents are related in this question. The answer is "I1 + I3 = I2", but can someone please explain according to the law "sum of currents in to the junction equal to out of the junction." How signs are put over here.

Next part: Why e.m.f's are subtracted in this question.. Aren't they to be added?

I am pretty much disappointed from my concepts of Kirchoff's law. Please help me to do this Question (taken from OCT/NOV 2011 - p22).

I'll be your grateful.

in the first part let us consider b as a junction so current entering B are ( I1 and I3) = current leaving junction B = I2
so I1+I3=I2

second one , loop HBFGH ....will be
E1=I1R1+I1r1+I2R2
Easy

for the next one you have to remember that the cell though which current LEAVES is the one having higher E value and always subtract the other one from it.

so it will be E1 - E2

i hope my answers are correct according to ms and hope you understood !!

 

[queen of the legend]

In the projectile motion?
when the ball is thrown upwards and it just touches the height of the wall.... will we take acceleration as -9.81 ? or +9.81 ?

like in this paper: http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w10_qp_22.pdf question 2 (a)(ii) they have taken s = ut - 0.5at^2 why "-" ? why not plus?

if the ball is traveling against the gravitational pull then its acceleration will be negative that is obvious!
but if you throw the ball from a height then g= + 9.8 ms^2

 

[queen of the legend]

can someone explain b iii

qp: http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w02_qp_2.pdf

ms: http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w02_ms_2.pdf

you did not specify the question !
is it about principle of superposition ??
if so :
principle of superposition of waves states that when two waves superimpose or overlap then the resultant displacement is sum of individual displacements.

 

[geek101]

you did not specify the question !
is it about principle of superposition ??
if so :
principle of superposition of waves states that when two waves superimpose or overlap then the resultant displacement is sum of individual displacements.

thnx i just drew my wave wrong

 

[queen of the legend]

please explain : question 4c ( 22/2010)

 

[ronaldo9252]

Please i need May/June 2012 Mathematics Alevel 31,32,33 exam papers ! URGENNTT

 

[Silent Hunter]

http://www.xtremepapers.com/papers/...and AS Level/Physics (9702)/9702_s07_qp_2.pdf

in question 1 (d) ... why have they put u = 0 ? cuz its says the electron travels initially at the given speed in part (c) .... so doesnt it mean that the u = 5.0 x 10^7 ? why 0 ?

thank you

 

[hussamh10]

http://www.xtremepapers.com/papers/...nd AS Level/Physics (9702)/9702_s10_qp_23.pdf
Q2 whole question plzzz sraw the vector diagram plllllllllzzzzzz help

 

[emkay]

please explain : question 5 ( 22/2010)

For Question#5(a)(i)
Use the data under the linear region of the graph, for stress/10^8 each block (2.5-2.0)/10 is of 0.05 so (0.05*3) + 2.0*10^8 (because 2.15 on the graph is the last point which cover's the linear region) i.e 2.1*10^8. For strain, take the same point of 2.15*10^8 of stress as vertical height and see where it coincides with the point on the horizontal line of strain. each block of strain (2.0-1.0)/10 is of 0.1 so (o.1*9) + 1 so it would be 1.9*10^3.
Young modulus: stress/strain i.e 2.15*10^8/1.9*^-3 = 1.1*10^11 Pa.

(ii) This was some Cambridge mistake, it wasn't included in the course.

(b) The area between the lines represents energy, when rubber is stretched and then released the two area's before and after are different i.e difference in the energies, this energy difference represents energy released as heat that would be either the pressure on the tyres of the car/ frictional force against the car or the weight of the tyres.

 

[emkay]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s10_qp_23.pdf
Q2 whole question plzzz sraw the vector diagram plllllllllzzzzzz help

Question#2
(a)
1. Sum of all the force's acting on the body must be zero.
2. Sum of moment of torque must be zero i.e sum of clockwise moment = sum of anti-clockwise moment.
(b)
(i) Force's with equal magnitude represented by the side of the triangle and the arrow used is for the direction, head to tail rule is applied here.
(ii) it show's cyclic vector's.
For further assistance, i have attached a picture.
(c)
In this part, take the readings from the scale i.e 1cm=1N so T1= 6.5N, T2= 4.7N.
(ps. the readings won't match ms, due to the size of paper used in past papers)
I have attached a picture for this as well.
(d)
Since the force's in string's are horizontal, there is no vertical force's to support the weight and hence, it is not possible to create tension in 7.0N of weight.

(Ps. my drawings are really bad, but i tried making it clear for you by editing a bit.

 

[Lyfroker]

How to calibrate a spring balance?

 

[aniroula]

Which factors affect the brightess and darkness of fringes except amplitude and distance(D) of the slits from the screen,,