106as it is a light string,
net torque and net force on it is zero.
if the tension were to act on any other direction than the direction of the string, net torque wont be zero about every point in space
In any arbitrary string,
can we take the tension along the direction of the string?
Justify...
Also, Can you give a similar analysis for a rod?
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11 Answers
106
62Why is it that the string is horizontal...
Your method is almost correct Asish :)
1@ashish : you specified " it is a light string"...
what if the string has some mass..
or did nishant bhaiyya forget to mention it in the question ?
62@ Philip.. and others..
No i din forget to say that the string is massless...
I just left it intentionally. to see how the answer changes due to the effect of the mass of the string..
and is it justified to make that assumption when mass is small..
33if it is massless its obvious F=ma
m=0 so F=0 hence T is along string....
This reply only to wake this post up.. :)
also torque is zero
1@ abhi :
net force = 0 does not imply that tension has to be taken along the string (eg ashish's post Ist fig.)
It is rather both arguments that m as well as I (the moment of inertia) will be zero implying that F as well as tau =0.
for a string with mass however tension may not be taken along the string always....
3i guess this might be the origin of the question.Direction of the zero vector.
24My view:
The source of tension in wire(light or heavy) will be net external force which tends to change in its basic stable orientation.
When a force F is applied the wire,the particles suffer acceleration,but the fibres of wire don't allow the same(we have studied all that in solids chapter).
So small tension vectors dT act opp to external force F
and the resultant of these forces will always be perpendicular to the cross section of string(becoz infinite vectors of same magnitude at an angle dθ will have resultant of T perpendicular only)
