What is wrong with this equation ?

[ManishR]

A block of mass m1 ϭ 2.00 kg and a block of mass
m 2 ϭ 6.00 kg are connected by a massless string over a pul-
ley in the shape of a solid disk having radius R ϭ 0.250 m
and mass M ϭ 10.0 kg. These blocks are allowed to move
on a fixed block-wedge of angle ␪ ϭ 30.0° as in Figure
P10.37. The coefficient of kinetic friction is 0.360 for both
blocks. Draw free-body diagrams of both blocks and of the
pulley. Determine (a) the acceleration of the two blocks
and (b) the tensions in the string on both sides of the
pulley.

[PLAIN]http://img820.imageshack.us/img820/9199/36360522.jpg

(m₁ + m₂)a = m₂gSin30 - $$\mu$$m₁g - $$\mu$$m₂gcos30

what is wrong with this equation ?

 

[Petr Mugver]

what is wrong with this equation ?

You neglect the momentum of inertia of the pulley.