Physics: Post your doubts here!

[Kanekii]

For Q 8 and 14 i have no clue

 

[A*****]

View attachment 64053 Something like this i assume

Yes I got it thanx alot!
Btw which path difference is this??

 

[A*****]

For Q 8 and 14 i have no clue

Its ok

 

[hellodjfos;s'ff]

View attachment 64046 View attachment 64047 View attachment 64048 View attachment 64049
View attachment 64050

Plz help

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.

 

[hellodjfos;s'ff]

View attachment 64046 View attachment 64047 View attachment 64048 View attachment 64049
View attachment 64050

Plz help

8 is a slightly tougher question. Throughout this question, the balloon is moving at a constant speed meaning the balloon is in equilibrium so upwards forces must be equal to downward forces. In the first situation, the balloon is going down so the air resistance(AR) and upthrust(UT) are acting upwards while the weight(W) is acting downwards. This making an equation, W=AR+UT. The question states that the AR has a value of F. The final equation becomes W=F+UT. For the 2nd situation, the balloon goes up, hence the W and AR act downwards while UT acts up. The equation for the 2nd equation is UT=W+AR. Now replaced W with the equation you found in the 1st situation and AR with F(as the question says). UT=F+UT+F. If you solve this equation, you will find that it would be 0=2F. This means that there is a resultant force of 2F acting downwards, so to balance it you must either produce a force of 2F acting upwards or remove a force of 2F acting downwards. The question states how much weight must be released from the balloon, so that means weight of 2F must be removed. This makes B the answer. There could be alternative methods to solve this question but I find this one to be the best.

 

[dwightedknight]

8 is a slightly tougher question. Throughout this question, the balloon is moving at a constant speed meaning the balloon is in equilibrium so upwards forces must be equal to downward forces. In the first situation, the balloon is going down so the air resistance(AR) and upthrust(UT) are acting upwards while the weight(W) is acting downwards. This making an equation, W=AR+UT. The question states that the AR has a value of F. The final equation becomes W=F+UT. For the 2nd situation, the balloon goes up, hence the W and AR act downwards while UT acts up. The equation for the 2nd equation is UT=W+AR. Now replaced W with the equation you found in the 1st situation and AR with F(as the question says). UT=F+UT+F. If you solve this equation, you will find that it would be 0=2F. This means that there is a resultant force of 2F acting downwards, so to balance it you must either produce a force of 2F acting upwards or remove a force of 2F acting downwards. The question states how much weight must be released from the balloon, so that means weight of 2F must be removed. This makes B the answer. There could be alternative methods to solve this question but I find this one to be the best.

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

 

[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.