Mechanics As level......

Thread starter 4 months ago
#1
questions where beads are threaded to a wire(be it smooth or rough) just don't make sense... at least not to me anyways.. if its threaded.. shouldn't the normal force act perpendicular to the bead? as in leftwards or rightwards... this is difficult to explain.. I'll send an attachment as an example......
0
Thread starter 4 months ago
#2
What I did was first draw the free body force diagram, with the normal force and weight acting vertically, and in opposite directions.. and I assumed that the horizontal component of tension in the string is equal to the frictional force... but I don't understand if the friction is supposed to act at some angle or just horizontal.. I came to the conclusion that it must be at some angle as I read in my text book, that in one of the modelling assumptions of beads, the beads can move up the thread.. so the friction must act to oppose motion... but then the lack of information in the question(or at least I think so) made it seem like my conclusion was incorrect.. and I have absolutely no idea what I'm supposed to do now... the value I got for the tension was 1.3N after assuming friction acts horizontally..

(Original post by mqb2766)
For reference, its from the 2019 exam and the MS will be available.
I looked it up.. but I can't seem to find it anywhere really..
0
4 months ago
#3
(Original post by Abraham_Otaku)
What I did was first draw the free body force diagram, with the normal force and weight acting vertically, and in opposite directions.. and I assumed that the horizontal component of tension in the string is equal to the frictional force... but I don't understand if the friction is supposed to act at some angle or just horizontal.. I came to the conclusion that it must be at some angle as I read in my text book, that in one of the modelling assumptions of beads, the beads can move up the thread.. so the friction must act to oppose motion... but then the lack of information in the question(or at least I think so) made it seem like my conclusion was incorrect.. and I have absolutely no idea what I'm supposed to do now... the value I got for the tension was 1.3N after assuming friction acts horizontally..

I looked it up.. but I can't seem to find it anywhere really..
Googling the question
https://qualifications.pearson.com/c...e_20190606.pdf

Friction opposes the direction of the motion so if the motion should be vertical it will act in that direction. Its maximum magnitude is given by mu multiplied by the normal (perpendicular) force. The usual, simple scenario of a block on a rough horizontal table is the weight is the nornal force and the maximum friction is mu*weight and this limits motion in the horizontal direction. Upload your diagram and any working for this question if you need anything more.
Last edited by mqb2766; 4 months ago
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