Physics: Post your doubts here!

[hassam]

thank you brother for clearing my cnfusion

 

[JD REBORN]

Q9 with proper explanation cuz i dont know what it is asking.
For Q26 why cant D be correct cuz at antinodes displacement is maximum ....???

 

[SkyPilotage]

Q9 with proper explanation cuz i dont know what it is asking.
For Q26 why cant D be correct cuz at antinodes displacement is maximum ....???

Q9
Its movin up and down. Lowest point of motion is at the bottom where the speed is zero!
Point D from the graph is the lowest point since the speed is increasing and is getting ready to move UP!
Q26
Yes , but the question is asking for vibrations not necessarily maximum vibrations!
At Nodes ! There are no vibrations.
At all the other points, there is! D stats that there is between antinodes. Between 2 antinodes there is a node where there is no vibratioN! so its wrong!

 

[anonymous123]

A ball is kicked towards goal posts from a position 20m from and directly in front of the posts. The ball takes 0.60 s from the time it is kicked to pass over the cross-bar, 2.5 m above the ground. The ball is at its maximum height as it passes over the cross bar. You may ignore the air resistance

a) Calculate the horizontal component of the ball's velocity

 

[darknessinme]

A ball is kicked towards goal posts from a position 20m from and directly in front of the posts. The ball takes 0.60 s from the time it is kicked to pass over the cross-bar, 2.5 m above the ground. The ball is at its maximum height as it passes over the cross bar. You may ignore the air resistance

a) Calculate the horizontal component of the ball's velocity

20/0.6=33.3 m/s

 

[Mustehssun Iqbal]

Assalamu alaikum,
How to solve Q.3 part b in June 2003, Paper 2??
http://www.xtremepapers.com/papers/...and AS Level/Physics (9702)/9702_s03_qp_2.pdf
Here's its marking scheme: http://www.xtremepapers.com/papers/...el/Physics (9702)/9702_s03_ms_1+2+3+4+5+6.pdf
Thanks!

 

[anonymous123]

20/0.6=33.3 m/s

i get the same ans but in ms its 2.5/0.6 = 4.17

 

[darknessinme]

i get the same ans but in ms its 2.5/0.6 = 4.17

The ms is wrong. They should've used 20m instead of 2.5m.

 

[farrukh]

pls solve this

 

[Zishi]

pls solve this

Assuming that you're facing a problem in part (a), the lowest wavelength photon would be emitted when an electron makes a transition from the ground state to "zero" level.

 

[farrukh]

Assuming that you're facing a problem in part (a), the lowest wavelength photon would be emitted when an electron makes a transition from the ground state to "zero" level.

i am confused that why are we using the zero level? why not the transition from -1.56 eV to -10.43eV

 

[Zishi]

i am confused that why are we using the zero level? why not the transition from -1.56 eV to -10.43eV

Because that is the Maximum Energy change we can get. According to E=hf max energy means maximum frequency, so minimum wavelength. Got it?

 

[farrukh]

thanks

 

[hmlahori]

http://www.xtremepapers.com/CIE/International A And AS Level/9702 - Physics/9702_w07_qp_1.pdf

Can anyone please explain Q 11 of this paper? Does the answer have anything to do with centripetal force?

 

[Zishi]

http://www.xtremepapers.com/CIE/International A And AS Level/9702 - Physics/9702_w07_qp_1.pdf

Can anyone please explain Q 11 of this paper? Does the answer have anything to do with centripetal force?

No, it isn't related to Centripetal force - you're not expected to know about it in an AS Level paper. B should be the answer, because that is the resultant of normal force and friction force on the tyre. Force of friction is in the same direction as car's motion because the tyre must be rotating in a clockwise direction.

 

[JD REBORN]

In Q5 why cant B and D be correct?
http://www.xtremepapers.com/papers/...and AS Level/Physics (9702)/9702_w06_qp_1.pdf

 

[CaptainDanger]

9702_w11_qp_11.pdf
9702_w11_ms_11.pdf

Q 4, 26 & 32?

 

[JD REBORN]

http://www.xtremepapers.com/papers/...nd AS Level/Physics (9702)/9702_w09_qp_12.pdf
Q11
For Q23 answer is B cuz speed of light in vacuum is constant.Is my reasoning correct or is their any other reason?

 

[JD REBORN]

9702_w11_qp_11.pdf
9702_w11_ms_11.pdf

Q 4, 26 & 32?

Q4
For L units are m,for time T s and radius a m.sin theta has no units.Now u put the units ignoring 3:
m(m^2/P)=Qs^2
Now if P has units m^2 and Q has ms^-2 then on both sides there will be m so thats why B is correct.
Q26
The length of cube is l,its area of crosssection is l^2 and force is F.Since young modulus is not given we assume it to be E.Now
E=Fl/delta l*l^2
delta lE=Fl/l^2
delta lE=F/l.Now this is the same as B option
Q32
The force acting on +Q is F=+QE
The force acting on -Q is F=-QE
Now since these forces are equal in magnitude and one has a negative sign so resultant force will be zero
The electric field is orginating from positive charges.So to make it easier assume that each arrow has a negative charge.Now +Q will be attracted to this charge and and -Q will be repelled so left side of rod will move upward(anticlockwise moments)

 

[smzimran]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w09_qp_12.pdf
Q11
For Q23 answer is B cuz speed of light in vacuum is constant.Is my reasoning correct or is their any other reason?

Yes,
Because speed of light (red or green) both are same and the wavelenghts different!
Using the formula:
c = f * lamda
We can imply that since wavelenghts are different, frequency must also be different !