# To estimate the required torque

1. Jun 19, 2009

### ravipatil666

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

2. Jun 19, 2009

### tiny-tim

Welcome to PF!

Hi ravipatil666! Welcome to PF!

Torque = distance "cross" force …

so what is the radius of the pulley?

3. Jun 19, 2009

### ravipatil666

f=m*g
r=.026
and T=f*r (N-m)
thats it?

4. Jun 19, 2009

### ravipatil666

and thanks 4 my post tiny-tim

5. Jun 19, 2009

### tiny-tim

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 )

6. Jun 19, 2009

### ravipatil666

oh ya my mistake....

7. Jun 19, 2009

### ravipatil666

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

8. Jun 19, 2009

### ravipatil666

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.

9. Jun 19, 2009

### tiny-tim

(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.
nothing … only the radius matters.

10. Jun 19, 2009

### Dr.D

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.

11. Jun 22, 2009