tough mechanics question...!!!

[hassam]

help me out with the last part

 

[Zishi]

Hey, I think this is an M3 question..it's really tough. Btw which board's question is this? Edexcel, AQA, or what?

I think you've solved all the papers of CIE already, and now you may be doing questions of M1 from different boards, etc? Am I right? If no, then may you please tell me how are you preparing for maths, cuz I've also completed all the CIE papers twice and there's no to practice now...

 

[ahmed t]

well if u finished the pastpapers twice without doubts then uve practiced enough in my opinion
anyway try the cambridge books a few tough ones in there

 

[hassam]

OCR...U try this question i solved it at last......

 

[Zishi]

@Hassam: I've also solved this question but wasn't confident with my answer. My acceleration of upper bl9ock is 4.09 ms^-2 and I get deceleration of lower block, are my answers right? Btw will you be doing questions from other exam boards after doing questions from OCR?

@Ahmed: I've heard that questions from CIE endorsed books are way too difficult, and those type of questions don't come in actual papers. :shock:

 

[hassam]

ur ansers are correct...bt u ll nt say deceleration for the lower block....u ll say a=0 because if friction is greater than object stays at rest and donot start to move backwards........

 

[Zishi]

ur ansers are correct...bt u ll nt say deceleration for the lower block....u ll say a=0 because if friction is greater than object stays at rest and donot start to move backwards........

Hmm, yeah I know that I'll be saying it won't move. It's just that as frictional forces are greater than forward forces, so it won't move.

 

[usman]

salam

hey check if these answers are ok?
(i) coefficient of friction = [8 + 5*sqrt(3)]/19
(ii) mu = [5*sqrt(3)]/13
(iii) a(upper block) = [50*sqrt(3) - 13]/18 ms^-2
a(lower block) = 0 ms^-2 since the magnitude of friction is greater than D.F.

 

[DragonCub]

(i) is really easy
Normal reaction = 12N - 5N * cos60 = 9.5N
Total tension = 4N + 5N * sin60 = 8.33N
Coefficient of friction = 8.33N / 9.5N = 0.877

(ii)
Upper one: tension = 5N * sin60 = 4.33N
Normal reaction = 9N - 5N * cos60 = 6.5N
coefficient of friction = 4.33N / 6.5N = 0.666

(iii)
......No idea. Really tough