SOURAV MISHRA
Last Activity: 11 Years ago
in case of ideal pulleys the tension on both sides of the pulley are same.
use constraint relationships.
these are based on the fact that the length of a string is constant.
write equations for this and differentiate them to get relations between the different velocities and accelerations.
remember that the velocity along a particular string must be same in case jerks and impulsive movements are absent.
you can also use the realtion that ∑T.a = 0 that is the sum total of the scalar products of the individual tensions and the corresponding accelerations equals zero.
this helps you find relation between tension forces, and accelerations given that some of these quantities are known.
you can also solve such problems logically. just imagine if one of the movable pulleys were displaced then by what length do the strings move and so you can know by how much the other movable pulleys move.
thus you can get a relation between the distances moved by the various movable pulleys.
remember that in case of a fixed pulley the distances moved by the string on both sides of the pulley are equal and opposite.
whenever question contains only ideal pulleys remember that even if some of them are moveble the net force and the net torque on all of these pulleys will always be zero since these are massless pulleys.
in case you come across pulleys which have mass remember that the net torque on these may not be zero.
for such pulleys where the actual situation appears that the pulley would be rotating the tensions on both sides of such a pulley are different and you have to account for the rotation of the pulley as well. but the acceleration of the thread passing on it will be same along its length.
remember the specail case of the ideal pulley where the string only slides over it and the pulley actually does not rotate.
for non ideal pulleys where slipping is absent the tangential speed of the pulley and the speed of the rope passing over it are same.
if you want to know the method then put up a question and you will get it completely solved step by step.
these are the basics to solve a question on pulleys.