1. ## pulleys

hi i am studying pulley systems in applied maths and i am wondering if there is a formula for the force exerted by a string on a pulley

2. ## Re: pulleys

It is the same as the force of the object on the string. There are a few "complications". This is, of course, if the object is not being [b]accelerated[/- the object is being held still or moved up or down at constant speed. And the force of the object on the string is the weight of the object divided by the number of vertical strings. In a "simple" pulley where the line goes up to the pulley, from the person holding it, then down to the object, the force on the string, and so the force of the string on the pulley is the weight of the object. If you have a "compound" pulley where the string goes, say, from the person holding it up to a pulley, then down to another pulley which is attached to the object. then back to terminate at the upper pulley, there are two vertical strings between the pulleys and one from the lower pulley to the object. The force of the object on the lower string, and so its force on the pulley, is the weight of the object. The force on each of the two strings between the pulleys, and so the force of the strings on the pulleys is the weight of the object divided by 2. The same idea for more complicated pulleys: divide the weight of the object by the number of vertical string supporting it at that point.

3. ## Re: pulleys

a question i am doing is A particle of mass 4 kg rests on a rough
horizontal table. It is connected by a
light inextensible string which passes over
a smooth, light, fixed pulley at the edge of
the table to a particle of mass 8 kg which
hangs freely under gravity.
The coefficient of friction between the 4 kg mass and the table is .25
The system starts from rest and the 8 kg mass moves vertically downwards.
find the force exerted by the string on the pulley. to work this out they use √(t^2+t^2).where t is the tension in the string. do you know why they do this

4. ## Re: pulleys

I don't believe there is enough information to solve this. Is anything said about the acceleration as the 8 kg mass moves?

5. ## Re: pulleys

it worked it out