# To estimate the required torque

a mass of 100N has to be lifted up via string attached to pulley.
What is the torque required to rotate that pulley

## Answers and Replies

tiny-tim
Science Advisor
Homework Helper
Welcome to PF!

a mass of 100N has to be lifted up via string attached to pulley.
What is the torque required to rotate that pulley

Hi ravipatil666! Welcome to PF!

Torque = distance "cross" force …

so what is the radius of the pulley?

the pulley has 26mm radius..
f=m*g
r=.026
and T=f*r (N-m)
thats it?

and thanks 4 my post tiny-tim

tiny-tim
Science Advisor
Homework Helper
the pulley has 26mm radius..
f=m*g
r=.026
and T=f*r (N-m)
thats it?

Yup! It's as easy as that!

(except that you don't need the "g", since the mass is given to you in newtons, not kg, anyway )

oh ya my mistake....

and i want to know when does the eq T=I*alpha
comes into picture???

and also 1 more question
wht happens if the width of the pulley s increased?
bcoz width has nothing to do in the eq only radius s considered.

tiny-tim
Science Advisor
Homework Helper
and i want to know when does the eq T=I*alpha
comes into picture???

(have an alpha: α )

ah, that's only if the pulley has non-negligible mass, and you want to find how fast it's rotating …

I is the moment of inertia of the pulley, and α is the angular acceleration.
wht happens if the width of the pulley s increased?

nothing … only the radius matters.

Increasing the width of the pulley will require more material which will increase the value of I, so the change will show up there, even though the width does not appear directly in any of the equations you have written.

thanks(dhanyawaad).........