A solid uniform disk of mass 21.0 kg and radius 85.0 cm is at rest flat on a frictionless surface A string is wrapped around the rim of the disk and a constant force of 35.0 N is applied to the string. The string does not slip on the rim.
1- When the disk has moved a distance of 5.5 m, determine how fast it is moving.
Kinetic energy= (mv^2)/2 Rotational kinetic energy = (Iw^2)/2 Work=Fdcos(theta)
The Attempt at a Solution
Since the object is at rest, I know that the initial kinetic energy of the disk is zero and that after applying a force it will have final kinetic energy both rotation and translation.
So my energy of conservation equation would be
Work done by pulling= Kinetic energy Translational + Kinetic energy Rotational
(35)(5.5) = v^2( (m/2) + (m/4)
When I solve for v, I get 3.49. But the answer is 4.3 m/s. Is my conservation of energy equation wrong?