Correct Answer - A
force due to pressure difference is `F=1/2 rhopiR^(2)(v_(2)^(2)_v_(1)^(2)) = (7rhopiR^(2))/2`
Now `F-f=Ma`
`fR=2/5MR^(2)xxa/R`
`Rightarrow f=2/5Ma Rightarrow f=2/7F=rhopiR^(2) Rightarrow mumg=pirhoR^(2)`
`Rightarrow mu=(pirhoR^(2))/(mg)=1/4=0.25`