A disc having uniform surface charge density +σ  in upper half and −σ in lower half is placed on a rough horizontal surface as shown in figure. A uniform electric field is set up as shown. If mass of disc is M and its radius is R, as well sufficient friction is present to prevent slipping, the acceleration of disc is

[Step 1]: Dipole moment  ∵σ=qA⇒q=σAhemisphere=σπR22​⇒P=2aq=σπR222.4R3π∵distance of com from surface either upwards or downwards, a=4R3π[Step 2]:  P=4R3σ3[Step 3]:  f=Ma[Step 4]:  τE−τf=Iα​⇒PE0−fR=Iα​⇒4R3σ3E0−MaR=MR2α2​⇒4R3σ3E0=MaR+MR2aR2∵For pure rolling, α=aR​⇒4R3σ3E0=3MRa2​[Step 5]:  For pure rolling, α=aR[Step 6]: For pure rolling  a=89σE0R2M