So I\'m having trouble even conceptualizing how to attack this particular proble

Question

So I'm having trouble even conceptualizing how to attack this particular problem. Basically, in my physics lab we were asked to calculate acceleration due to gravity of a single pulley system where a cart is attached to a counterweight which hangs over the edge of table.(Fig 1). Friction is negelected in this experiment.  I understand how to calculate the acceleration from the two masses and the force of gravity and that isn't the part I'm worried about.

We are asked to calculate all uncertainties with this experiment and the particular uncertainty I'm unsure about is the uncertainty associated with the mass of the string which we found to be 2 grams +/- 0.05 grams. Wouldn't the mass of the string alter the acceleration slightly since more and more of its mass is affected by gravity as its passes over the pulley and becomes vertical? If so, how would one quantify this change?

I apologize in advance if this description is too vague. Let me know if any more information is needed!

So I'm having trouble even conceptualizing how to attack this particular problem. Basically, in my physics lab we were asked to calculate acceleration due to gravity of a single pulley system where a cart is attached to a counterweight which hangs over the edge of table.(Fig 1). Friction is neglected in this experiment. I understand how to calculate the acceleration from the two masses and the force of gravity and that isn't the part I'm worried about. We are asked to calculate all uncertainties with this experiment and the particular uncertainty I'm unsure about is the uncertainty associated with the mass of the string which we found to be 2 grams +/- 0.05 grams. Wouldn't the mass of the string alter the acceleration slightly since more and more of its mass is affected by gravity as its passes over the pulley and becomes vertical? If so, how would one quantify this change?

Explanation / Answer

Hi,

If you consider a spring with mass. The problem becomes very tough to do since if it is not an ideal string the Cart and the weight will also havedifferent acccelerations. In most of the cases we take the mass of the string as well as the pulley negligible and frictionless (pulley). As for uncertainties, I think what they mean is uncertainties in measuring just mass of the blocks and accelerations.

The question is not very vague but rather is a very intersting one. But it is an unnecessary complication to take the mass of the spring. Especially if the masses are in the range of 1kg and the force due to a weight of a 2g string would be negliglible.

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