AS Physics P1 MCQs Preparation Thread.

[Martee100]

Can some one help in this?

I just dont understand relative speed in collisions!

 

[rockerkunal]

Can someone please explain me how to do Q24..​

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s12_qp_11.pdf

use the young's modulus equation.. after simpificaiton you should get Y=FL/Ax, open A it will be pi. D^2/4, make x subject, get x= (4FL)/(pi.D^2Y)
do the same for the next one, but instead of L use 3L and instead of A being that, it will be pi.D^2 after cancleing out the 4s, make extention subject, then devide the first extention to the new extention, obtain x/e = 4/3, x=3/4 get it?

 

[ruler_of_the_world]

Good luck guys. (Y)

 

[rockerkunal]

i

Can some one help in this?

I just dont understand relative speed in collisions!

are you sure its D cuz by my calc it should be A.. :S

 

[Obsidian Fl1ght]

read this http://science.hq.nasa.gov/kids/imagers/ems/waves3.html

Thanxx again

 

[Obsidian Fl1ght]

crap! those trixy little cie people! smh.. thanks a ton man

Glad to help.

 

[Martee100]

i
are you sure its D cuz by my calc it should be A.. :S

Thats what! I also selected A

 

[Martee100]

 

[rockerkunal]

Thats what! I also selected A

woaah. did cie screw up? need expert advice.

 

[Sajeeb Chowdhury]

http://papers.xtremepapers.com/CIE/...nd AS Level/Physics (9702)/9702_s12_qp_12.pdf q14 ny1

 

[rockerkunal]

okay, according to me, the reaction cannot change direction since the center of mass is unaltered. so that rules out c and D and since the ladder has to move vertically downward, the reaction at the top should be upwards.. if its A then it wouldnt move down at all it would come out of the wall.. well thats my pushing theory, anyone got a better one?

 

[lee mee..]

use the young's modulus equation.. after simpificaiton you should get Y=FL/Ax, open A it will be pi. D^2/4, make x subject, get x= (4FL)/(pi.D^2Y)
do the same for the next one, but instead of L use 3L and instead of A being that, it will be pi.D^2 after cancleing out the 4s, make extention subject, then devide the first extention to the new extention, obtain x/e = 4/3, x=3/4 get it?

why are we dividing both extensions ?

 

[rockerkunal]

see you guys in like 7 hours, im going to bed, best of luck everyone! chill, dont panic

 

[rockerkunal]

why are we dividing both extensions ?

to get the ratio. otherwise we wont get a pure number

 

[6Astarstudent]

i
are you sure its D cuz by my calc it should be A.. :S

relative speed of approach = relative speed of seperation, lots of students get confused by this question because there is no solid formula
note its speed not velocity.
speed of approach for this question you add U1 and U2 because they're coming towards each other.
seperation because they're going in same direction, you use the faster one (in this case V2) minus V1 so correct answer is D

In short, if the masses are in same direction (either before or after collision) you subtract the smaller one from the bigger one.
and if masses are in opposite directions you simply add the speed of the masses

 

[lee mee..]

to get the ratio. otherwise we wont get a pure number

ohh.. okkk ..... thank you

 

[Sajeeb Chowdhury]

okay, according to me, the reaction cannot change direction since the center of mass is unaltered. so that rules out c and D and since the ladder has to move vertically downward, the reaction at the top should be upwards.. if its A then it wouldnt move down at all it would come out of the wall.. well thats my pushing theory, anyone got a better one?

i did n't get a word u just said....

 

[6Astarstudent]

okay this question is really simple if you read the words.
Frictionless ground and rough wall. since ground is frictionless so R will be vertically upwards because there is no horizontal component, it is only reaction to balance the weight
that eliminates C/D leaving AB. then its a rough wall meaning there is friction so P must not be perpendicular to the wall as there is both vertical and horizontal component so answer is B


but what if the question contains 2 choices where in one, P is directed upwards and in one P is directed downwards? read the line "begins to slide" meaning its going downwards so the friction force will act upwards.

 

[rockerkunal]

relative speed of approach = relative speed of seperation, lots of students get confused by this question because there is no solid formula
note its speed not velocity.
speed of approach for this question you add U1 and U2 because they're coming towards each other.
seperation because they're going in same direction, you use the faster one (in this case V2) minus V1 so correct answer is D

In short, if the masses are in same direction (either before or after collision) you subtract the smaller one from the bigger one.
and if masses are in opposite directions you simply add the speed of the masses

Oh Physics...

 

[Sajeeb Chowdhury]

could ny 1 please solve this....