Physics: Post your doubts here!

[Autumn98]

Please help me with....I need clear reasoning too.....

 

[Mathemagical]

Thanks! But even if Q is moving fastest, it's at equilibrium position, so why won't its displacement be zero?

You're thinking of a stationary wave. This is a progressive wave, so there are no nodes where displacement is zero.

 

[nehaoscar]

is it B? if not, can someone explain please

No it's A
v = w - u
so just change the arrowhead direction on u so it is -u (towards north)
and form a normal triangle by joining the arrows

 

[zainab345]

Guys does anyone know any website where i could find some helpful notes on the physics practical?

 

[Hassansheikh]

how to calculate percentage uncertainty in As'level practical?

 

[princess Anu]

Ans: 9C, 4C 22 C

Doubts; Q4: why is it 1.1mg? shouldn't it be 1 mg.. as the car is accelerating horizontally ONLY so the vertical forces must be balanced to give 0 resultant & hence 0 acc in the vertical plane?
Q9 : I didn't get it at all .. why won't the period increase for R as well?
Q22 I tried all the calculations I could, but I couldn't get 0.07J .. Here is one of those;

1/2 * k * x^2
1/2 * ( 6/0.03)* 0.01^2
ans = 0.01 :/

Somebody help please!?

 

[qwertypoiu]

View attachment 54447 View attachment 54448 View attachment 54449


Ans: 9C, 4C 22 C

Doubts; Q4: why is it 1.1mg? shouldn't it be 1 mg.. as the car is accelerating horizontally ONLY so the vertical forces must be balanced to give 0 resultant & hence 0 acc in the vertical plane?
Q9 : I didn't get it at all .. why won't the period increase for R as well?
Q22 I tried all the calculations I could, but I couldn't get 0.07J .. Here is one of those;

1/2 * k * x^2
1/2 * ( 6/0.03)* 0.01^2
ans = 0.01 :/

Somebody help please!?

The car has to do two things: make the boy accelerate forward with a force of 0.5g, and also provide the contact force upwards needed to counter his weight pulling him down with the force of 1g. The resultant of these two forces (left and up) will be diagonally left-up as shown and will have the magnitude of sqrt(1^2 + 0.5^2) = 1.118g

As for the pendulum, the only real thing that affects it is the length of the string. The reason why mass is not included is just like why two objects with different masses have the same gravitational acceleration. Although force is proportional to mass, acceleration is inversely proportional. What I'm saying is, the bob has angular acceleration due to gravity, and gravitational acceleration is not affected by mass.


Look at this image. It shows the area you should be calculating... The extra strain energy after having extended it by 0.03m already using a 6N load, and then extending it by 0.01 further. It's a trapezium, or difference of area between two triangles.

 

[princess Anu]

The car has to do two things: make the boy accelerate forward with a force of 0.5g, and also provide the contact force upwards needed to counter his weight pulling him down with the force of 1g. The resultant of these two forces (left and up) will be diagonally left-up as shown and will have the magnitude of sqrt(1^2 + 0.5^2) = 1.118g

As for the pendulum, the only real thing that affects it is the length of the string. The reason why mass is not included is just like why two objects with different masses have the same gravitational acceleration. Although force is proportional to mass, acceleration is inversely proportional. What I'm saying is, the bob has angular acceleration due to gravity, and gravitational acceleration is not affected by mass.

View attachment 54450
Look at this image. It shows the area you should be calculating... The extra strain energy after having extended it by 0.03m already using a 6N load, and then extending it by 0.01 further. It's a trapezium, or difference of area between two triangles.

Thanks A lot

Can you please also explain why can't we use 1/2 K*x2 formula for strain energy here? Or if we can use it , the way I have used it gives me a wrong answer, why.?

Thanks Again !

 

[princess Anu]

Q10. C is not correct which implies there are some other sort of energies at R.. which ones can they be?? :s
Q28 ans is C..can someone explain why not the others?

 

[amal sharkawi]

CAN ANYONE ANSWER PLZZZZ????

 

[princess Anu]

someone help please... ans is A

 

[syafiq izuddin]

anyone have any idea for physic paper 34 tomorrow?? OMG! Hopefully, electricity won't come out >> im suck alots for that topic!

 

[qwertypoiu]

Thanks A lot

Can you please also explain why can't we use 1/2 K*x2 formula for strain energy here? Or if we can use it , the way I have used it gives me a wrong answer, why.?

Thanks Again !

k = 6/0.03 = 200
You must realise that the spring is already stretched so has some energy already. Now you're adding energy to it by stretching it to 0.04. So you must find:
energy added = [total energy in spring when stretched to 0.04] - [total energy in spring when stretched to 0.03]
= 1/2 * 200 * 0.04^2 - 1/2 * 200 * 0.03^2
= 0.07J

 

[Amandaissocoollike]

October/November 2014 31 Q1 (f) someone please explain this to me, I never got the hang of this question

 

[Sahil Gupta]

Answer is B,.
Explain with working someone plz

 

[Maayee]

http://onlineexamhelp.com/wp-content/uploads/2013/11/9702_w12_qp_13.pdf
can someone pls help me with question 33, the answer is D

 

[Mathemagical]

http://onlineexamhelp.com/wp-content/uploads/2013/11/9702_w12_qp_13.pdf
can someone pls help me with question 33, the answer is D

Area = π*R²
Area 1= π*0.5² =π*0.25
Area 2 = π*0.25² =π*0.0625

Area 1 = 4* Area 2

Since Volume is constant, L is 4 times.

Resistance is 4*4 times 0.2, which is 3.2.

 

[amal sharkawi]

CAN ANYONE ANSWER PLZ ????/??

 

[DESTROYER1198]

HELP PLZZZ is the extension of a spring inversely proportional to the diameter or the diameter squared

 

[Abdul Hanan]

These are the toughest physics MCQs for me.. please explain thanks.

just try them if you have not already