Question

A solid spere of mass M and radius R is kept on rough surface the velocities of air (density p) around the sphere are as shown in figure Assuming R to be small and M`=(4pirhoR^(2))/g kg` what is the minimum value of coefficient of friction so that the sphere starts pure rolling? (Assume force due to pressure difference is acting on centre of mass of the sphere)

A. `0.25`
B. `0.50`
C. `0.75`
D. `1.0`

Answer 1

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`