See , it is a long prob . So hang on
Let the ring is at a distance x above the gnd
So extension in the spring = sqrt( x ^2 + ( 2 R ) ^2 ) - 2R
Tension in the spring = 4mg/ R * extension
Let the angle made by the spring to the horizontal be @
So , The comp Fsin @ adds the accelaration of the ring ( along with mg ) & comp. Fcos @ gives the normal force on the spring . So the frictional force is
F cos @
Now , from geometry
cos @ = 2R / sqrt( x^2 + ( 2R)^2 )
sin @ = x / sqrt( x^2 + ( 2R ) ^2 )
Now the eqn of motion for the ring is
mv dv/dx = mg -
Fcos @ + F sin @
after putting the values and on simplification this becomes v dv = g dx - 8
g { dx - 2r dx / sqrt ( x^2 + (2R)^2 } + 4g/R { x dx - 2R x dx/ sqrt ( x^2 + ( 2R)^2 }
integrating the above from 0 to 3 R / 2 and putting v^2 = 3 g R we get
= 1 / { 16 ( 1.5 - ln 4 ) } = 0.549