Solving the Yo-yo Problem: Final Velocity Calculation

[meanswing]

Homework Statement

A yo-yo has mass of 400 kg and radius of 1.5m. Its axle of rotation has a radius of 0.1m. Its string is attached to a crane. What is its final velocity after it is released.
mass (m)=400 kg
Radius (R)= 1.5 m
axle of yo-yo (r)= 0.1 m
height (h)=57m
angular acceleration (x)= x

Homework Equations

F=ma; I=(1/2)mr^2; a=xr a/r=x

The Attempt at a Solution

F=ma ; Torque=Tr=Ix T=Ix/r

Fnet,y = mg - T = ma

mg - I(a/r)/r = ma

mg = ma + I(a/r)/r

mg/ (m + I/r^2) = a

mg/(m + (1/2)mr^2/r^2 ) = a

a = 6.53 m/s

This doesn't seem right. Can anyone show me my error?

 

[RoryP]

well you have calculated the accelertion whereas the question asks for final velocity ...

 

[meanswing]

lol . ok figured it out. i was also using lowercase r instead of uppercase R.