Physics: Post your doubts here!

[Nibz]

help me in oct nov 11
q-26
ans is b
Nibz

∆L is basically compression.
L = Original length
When compression increases, original length decreases - fact - hence, inverse proportionality.

You can also prove it like this:
Strain = extension/original length => e / L
Compression = 1/e
Therefore, strain = 1/eL
When you look at this equation, you'll see that 1/e (compression ∆L) and L are inversely proportional.

 

[HongYue]

http://papers.xtremepapers.com/CIE/...nd AS Level/Physics (9702)/9702_w10_qp_11.pdf
Question 9

Can you help me too ? Nibz

 

[Tkp]

∆L is basically compression.
L = Original length
When compression increases, original length decreases - fact - hence, inversely proportionality.

You can also prove it like this:
Strain = extension/original length => e / L
Compression = 1/e
Therefore, strain = 1/eL
When you look at this equation, you'll see that 1/e (compression ∆L) and L are inversely proportional.

U truly are a genius.i was stuck in this prblm frm yesterday.May God help u to achieve success in ur life.Thnk u

 

[Tanvir Azad]

Thankyou very very much

so did u get it?

 

[Nibz]

http://papers.xtremepapers.com/CIE/...nd AS Level/Physics (9702)/9702_w10_qp_11.pdf
Question 9

Can you help me too ? Nibz

Use v^2 - u^2 = 2as
v has to be zero, since the train has to come to rest eventually.
s = x
The equation becomes: 2ax + u^2 = 0
make 's' distance the subject:
x = - (u^2)/2a
deceleration, i.e -a, is constant in the question.
take the constants out,
you get this relation: x ∝ u^2, i.e, s varies as the square of u.
So when u is increased by 20% (120/100 = 1.2), x will change by (1.20)^2 = 1.44x

 

[Sk. Shahriar Hossain]

Plz someone help me with Q no. 15, 19, 26, 32 & 37.....this is the link to the QP:
http://papers.xtremepapers.com/CIE/...nd AS Level/Physics (9702)/9702_s11_qp_13.pdf

 

[uzinova]

A particle of mass 2m and velocity v strikes a wall.
The particle rebounds along the same path after colliding with the wall. The collision is inelastic.
What is a possible change in the momentum of the ball during the collision?
A mv B 2mv C 3mv D 4mv

please help.

 

[Usman04]

Firstly, if there are 300 lines in 1mm then there would be 300 x 1000 lines in 1meter .. therefore D is 1/300000.
taking lamda as @..
n@= d sin&
put in the values of @ and d.
and take the value of sin@ as 1 because thats the value for the maximum angle
Find N.. it is somewhat 4.84
Thing is this was for only one side of the screen as angles are taken from the mid point in between the slits and thus the same number of maxima would be formed on the other side of the mid point between slits.. thus 4.76 x 2= 9.65 but as maximA OCCURS AT WHOLE NUMBER of N,, the maximum number of maxima is 9.

Firstly, if there are 300 lines in 1mm then there would be 300 x 1000 lines in 1meter .. therefore D is 1/300000.
taking lamda as @..
n@= d sin&
put in the values of @ and d.
and take the value of sin@ as 1 because thats the value for the maximum angle
Find N.. it is somewhat 4.84
Thing is this was for only one side of the screen as angles are taken from the mid point in between the slits and thus the same number of maxima would be formed on the other side of the mid point between slits.. thus 4.76 x 2= 9.65 but as maximA OCCURS AT WHOLE NUMBER of N,, the maximum number of maxima is 9.

thanks for clearing my problem but what will we do if he asks drk fringes or minima???

 

[white rose]

24)http://www.s-cool.co.uk/a-level/phy...finitions-of-stress-strain-and-youngs-modulus
We know that E is inversely proportional to the area, and directly proportional to the length.
Now, when we increase the length to 3L, the extension also increases 3 times → 3x.
But becoz we increase the diameter to 2D, we have increased the area by 4 times. A = π(d/2)^2 → A is now 4A.
And since extension is INVERSELY proportional to area, the extension now falls → x/4

So, the new wire's extension = 3x/4
Ans = B

Hope u gt it!
All credit to Nibz

Jazakallah khair....

 

[Usman04]

A particle of mass 2m and velocity v strikes a wall.
The particle rebounds along the same path after colliding with the wall. The collision is inelastic.
What is a possible change in the momentum of the ball during the collision?
A mv B 2mv C 3mv D 4mv

please help.

simple in question he says the collision is inelastic so kinetic energy is not conserved. Speed also changes because in inelastic collision speed decreases. so change in momentum = m1v1 - {-m2v2} 2mv-{-2m * v/2}
2mv-{-mv} when u solve it u get 3mv c is the coorect option

 

[hope4thebest]

Anyone what actually is viscous force or viscosity?Saw some mcq's related with viscosity

 

[white rose]

30)http://www.s-cool.co.uk/a-level/physics/diffraction/revise-it/diffraction-from-a-diffraction-grating
nλ = dsinΘ
Now, n = 1/(1 * 10^-6) → 1 * 10^6
Also, the angle of 70° is btw the 2 maxima so, the angle from the centre = 70/2 → 35°
Applying the formula,
λ = sin 35/(1 * 10^6)
λ = 574 nm

Ans = C
Hope u gt it!
All credit to Nibz.

this ques. is nt clear to me...the formula for lambda@ is n@=dsintita....but here u r dividing sin35/(1*10^6)...how??

 

[sara kamal]

http://papers.xtremepapers.com/CIE/...and AS Level/Physics (9702)/9702_s05_qp_1.pdf
please explain Q16 and 29

 

[white rose]

30)http://www.s-cool.co.uk/a-level/physics/diffraction/revise-it/diffraction-from-a-diffraction-grating
nλ = dsinΘ
Now, n = 1/(1 * 10^-6) → 1 * 10^6
Also, the angle of 70° is btw the 2 maxima so, the angle from the centre = 70/2 → 35°
Applying the formula,
λ = sin 35/(1 * 10^6)
λ = 574 nm

Ans = C
Hope u gt it!
All credit to Nibz.

i think u frgot q. 12...

 

[hope4thebest]

HELP PEOPLE

 

[suryashekhar]

A railway engine accelerates a train of total mass 800 tonnes (1 tonne = 1000 kg) from rest to a
speed of 50 m s–1.
How much work must be done on the train to reach this speed?A 1.0 × 106 J B 2.0 × 106 J C 1.0 × 109 J D 2.0 × 109 J

 

[snowbrood]

http://papers.xtremepapers.com/CIE/...nd AS Level/Physics (9702)/9702_s10_qp_11.pdf Q36 anyone help please

 

[Jiyad Ahsan]

Anyone what actually is viscous force or viscosity?Saw some mcq's related with viscosity

viscosity relates somewhat to the fluidity of a fluid (in our case, liquids).. it sort of describes a fluids resistance to flow
for example
Oil is a more viscous fluid (compared to water), it flows slowly and when you take Oil in a bottle, put an object on its surface and it will move down quite slowly.. that force that sort of resists the force of gravity pulling the object down is the viscous force.
On the other hand water flows more easily and has a smaller viscous force.
imagine swimming, you would find it easier to swim in water than in Oil, since Oil would put up a lot of resistance (viscous force) against your movement
In most cases, you may assume that a denser liquid will be more viscous and hence have a higher viscous force

 

[white rose]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s10_qp_11.pdf Q36 anyone help please

find the total resistance including the ammeter resistance....the lowest value of resistance means the higher is the current..they r inversly proportional

 

[hope4thebest]

viscosity relates somewhat to the fluidity of a fluid (in our case, liquids).. it sort of describes a fluids resistance to flow
for example
Oil is a more viscous fluid (compared to water), it flows slowly and when you take Oil in a bottle, put an object on its surface and it will move down quite slowly.. that force that sort of resists the force of gravity pulling the object down is the viscous force.
On the other hand water flows more easily and has a smaller viscous force.
imagine swimming, you would find it easier to swim in water than in Oil, since Oil would put up a lot of resistance (viscous force) against your movement
In most cases, you may assume that a denser liquid will be more viscous and hence have a higher viscous force

Thanks brother for the explanation!