Tension on a massless pulley homework.

[Crystal037]

Homework Statement

How come tension would act if the pulley is massless? also, can you tell me how the tension varies along a string

Relevant Equations

tension depends on distance...

please explain

 

[berkeman]

Welcome to the PF.

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[Crystal037]

please explain

it is the case when a string is around a pulley and two masses are there on either side of pulley
also how come tension act if we consider the rope to be massless as well

 

[Master1022]

it is the case when a string is around a pulley and two masses are there on either side of pulley
also how come tension act if we consider the rope to be massless as well

The point about the pendulum being light is so that the tensions on both sides can be assumed to be the same. If there is a mass, then we would need to worry about its moment of inertia and the tensions on both sides would not necessarily be the same.

In these types of pulley mechanics questions, tension doesn't depend on distance. In fact, if we make the assumptions that the:
- pulley is frictionless (no friction acting)
- pulley is light (no torque to accelerate the pulley)
- string is light (no force needed to accelerate the string)

then the magnitude of the tension is the same everywhere in the string. This is because we assume the string has no mass.

Why is there tension?
Not sure if I have the best explanation here. The block is going to pull down on the rope and therefore will exert a force on the string. One can exert a force on an object irrespective of its mass.

Quick read that might help as well: https://www.physicsforums.com/threads/tension-in-a-massless-string.708085/

Hope that was of some help

 

[haruspex]

How come tension would act if the pulley is massless? also, can you tell me how the tension varies along a string

Relevant Equations. tension depends on distance...

There must be tension or both masses would fall with acceleration g. Do you mean, how can tension be different on the two sides? It can be different if the pulley has mass (and is accelerating) or there is axial friction.

Tension can only vary along the string (on one side of the pulley) if the string has mass and is accelerating.

If this does not answer your question, please post the entire problem as given to you, together with whatever answer or method is confusing you.