Physics: Post your doubts here!

[dwightedknight]

Please post any paper 12 predictions

 

[A*****]

I'll do 14 first since it's easier. Take the axle as your pivot in this question. Now the issue with this question is that people don't understand where the 90N force is acting. I have attached a file to show where it's acting. The reason it's acting there is bc to move the vehicle forwards, there needs to be an anticlockwise moment so that the vehicle is pushed forwards. Now you know that all the forces and where they act, so just apply the principle of moment, clockwise moments=anticlockwise moments. Keep in mind that you don't where the man's weight will be acting when the vehicle applies a force, so that's what you will find in the calculation. This means: 600(200)=600(x)+90(400). You find that your x will be 140 mm. Since the man was initially standing 200 mm behind the axle and is now standing 140 mm behind it means that me moved 60 mm forwards making B the answer.

But doesn't the question say that the force acting is horizontal?

 

[hellodjfos;s'ff]

But doesn't the question say that the force acting is horizontal?

Oh yeah sorry, the force should be acting horizontally, not vertically, but it still produces an anticlockwise moment. That doesn't change any of the calculations. I've attached a corrected file showing where the 90N force would be acting.

 

[hellodjfos;s'ff]

I can only dream of answering the questions that you find difficult .

This question is not found difficult just by me, but by everyone! Haha.

 

[hellodjfos;s'ff]

Please post any paper 12 predictions

If anyone can post the paper 22 or give me all the questions from it, I can give solid predictions on what would come up as the topics from which questions are chosen are often interlinked for paper 1, 2 and 5.

 

[blymphocytes]

I have forgotten how to get resultants.......bcoz of stupid breaks.
Please help
number 2

 

[hellodjfos;s'ff]

I have forgotten how to get resultants.......bcoz of stupid breaks.
Please help
number 2

So you draw a vector diagram for this question. You connect the tail of one of the vectors to the head of the other vector, and connect the tail of the first vector to the head of the 2nd to get the resultant. I have shown this in the attachment. You will realize that the angle between the two vectors is 60 and the vectors have the same magnitude, hence it is an equilateral triangle meaning all the sides and angles have the same magnitude. So the resultant becomes 10N as well. If you find this difficult to understand, apply the cosine rule instead. You will find that the answer is 10N again(B).

 

[blymphocytes]

So you draw a vector diagram for this question. You connect the tail of one of the vectors to the head of the other vector, and connect the tail of the first vector to the head of the 2nd to get the resultant. I have shown this in the attachment. You will realize that the angle between the two vectors is 60 and the vectors have the same magnitude, hence it is an equilateral triangle meaning all the sides and angles have the same magnitude. So the resultant becomes 10N as well. If you find this difficult to understand, apply the cosine rule instead. You will find that the answer is 10N again(B).

Omg yeah...makes sense!
thanks i got it

 

[dwightedknight]

This question is not found difficult just by me, but by everyone! Haha.

Well that is sort of implied if you are a genius and find some thing difficult

My utmost respect to anyone going to KGS

 

[A*****]

Oh yeah sorry, the force should be acting horizontally, not vertically, but it still produces an anticlockwise moment. That doesn't change any of the calculations. I've attached a corrected file showing where the 90N force would be acting.

U are great if u don't mind, can I ask a few more?

 

[Mush999]

Pls help!
A voltage is carefully measured with a high-quality instrument and found to be 2.321V.
Two students, using two different methods, conclude that the voltage is 2.33V and 2.344V
respectively.
Which statement is correct?
A 2.33V is less accurate and less precise than 2.344V.
B 2.33V is less accurate and more precise than 2.344V.
C 2.33V is more accurate and less precise than 2.344V.
D 2.33V is more accurate and more precise than 2.344V.

 

[hellodjfos;s'ff]

U are great if u don't mind, can I ask a few more?

Yeah sure. It would be good for my revision too.

 

[A*****]

Yeah sure. It would be good for my revision too.

Both of them please

 

[hellodjfos;s'ff]

Pls help!
A voltage is carefully measured with a high-quality instrument and found to be 2.321V.
Two students, using two different methods, conclude that the voltage is 2.33V and 2.344V
respectively.
Which statement is correct?
A 2.33V is less accurate and less precise than 2.344V.
B 2.33V is less accurate and more precise than 2.344V.
C 2.33V is more accurate and less precise than 2.344V.
D 2.33V is more accurate and more precise than 2.344V.

Precision is the number of decimal places to which a measurement is taken, while accuracy is the closeness of the measurements to the actual values. So 2.33 is more accurate(closer to 2.321, you can find this out by subtracting the measurement and the actual value), while 2.344 is more precise since it's measured to a greater number of decimal places. This makes C the answer.

 

[Mush999]

Precision is the number of decimal places to which a measurement is taken, while accuracy is the closeness of the measurements to the actual values. So 2.33 is more accurate(closer to 2.321, you can find this out by subtracting the measurement and the actual value), while 2.344 is more precise since it's measured to a greater number of decimal places. This makes C the answer.

Thank you so much brother!

 

[A*****]

Does frequency need to be the same for two waves to be coherent?

 

[hellodjfos;s'ff]

Both of them please

View attachment 64061

For 36, you have to apply kirchhoff's 2nd law. There are two points where the voltmeter is connected, I will name the point on the right, A and the one on the left, B. So at A, the pd is E because it just came out of the cell and hasn't been used up(I am treating the internal resistances as resistor so that it's easier). This means that the pd at B must also be E since the potential difference is zero between these points. This means that the E at A was used up by the r1 since the more pd(also E) came out of the new cell. So now we can form 2 equations. First one: E=Ir1(just using V=IR), second: 2E=E+I(r2+R) which simplifies to become: E=I(r2+R). Now I can solve them simultaneously. I replace the E in E=I(r2+R) with Ir1(which is my other equation, E=Ir1).
This becomes Ir1=I(r2+R) ----> r1=r2+R ----> r1-r2=R making B the answer.

 

[hellodjfos;s'ff]

Thank you so much brother!

No probs bro

 

[hellodjfos;s'ff]

Does frequency need to be the same for two waves to be coherent?

Not necessarily, if waves need to be coherent, they must have a constant phase difference. Usually when waves are produced to be coherent they use the same source to produce the waves so yes, mostly they have the same frequency but it's not required.

 

[A*****]

Two wires with the same Young modulus E and cross-sectional area A, but different lengths L,
are subject to different tensile forces F. The extension e of each wire is the same.
The column headings in the table show four different quantities.
Which quantities have the same value and which quantities have different values for the two
wires?

FL/e. Ae/L. E/FL
A different differen same
B different same same
C same different different
D same different same

If u rearrange the equation E= Fl/Ae by making Fl/e the subject, it would be Fl/e= EA, since E and A are same for both so Fl/e would also be the same
Next make Ae/l the subject, Ae/l= F/E... E is same but F is different for both so F/E and hence Ae/l would be different
E/Fl= 1/ Ae A and e are same so E/Fl would also be same