Simple concept help: Pulley and Net Torque

[john562]

Homework Statement

A ball (hollow sphere) of radius .11m and mass .444kg is mounted on a frictionless axle. A massless cord is wrapped around the ball supporting an object of mass .02kg. Find the angular acceleration of the wheel, linear acceleration of the object and tension in the cord.

Homework Equations

The Attempt at a Solution

$$\Sigma$$F=F_g+T=m*a
-.2+T=.02a

$$\Sigma$$$$\tau$$=F*r=I*$$\alpha$$
-T*.11=(.0036*a)/.11
T = -.2975*a

-.2 + .2975*a = .02*a
-.2 = -.2775a
.72 = a

That's what I tried, but it's wrong.
Can anyone help?

 

[PhanthomJay]

Homework Statement

A ball (hollow sphere) of radius .11m and mass .444kg is mounted on a frictionless axle. A massless cord is wrapped around the ball supporting an object of mass .02kg. Find the angular acceleration of the wheel, linear acceleration of the object and tension in the cord.

Homework Equations

The Attempt at a Solution

$$\Sigma$$F=F_g+T=m*a
-.2+T=.02a

0.2 -T = .02a

$$\Sigma$$$$\tau$$=F*r=I*$$\alpha$$
-T*.11=(.0036*a)/.11

T*.11 = .0036a/.11

T = -.2975*a

T = .2975a

-.2 + .2975*a = .02*a
-.2 = -.2775a
.72 = a

That's what I tried, but it's wrong.
Can anyone help?

You must watch your signage. The acceleration is downwards. Choose the downward and clockwise directions as positive, for compatability and simplicity.