Correct Answer - D
Let the length of inclined plane be `d`. Speed of the block at the bottom of the upper half
`v = sqrt( 2 g sin 45^(@) xx (d)/(2)) = sqrt( g sin 45^(@) xx d)`
For the lower half , retardation : `( g sin 45^(@) - mu g cos 45^(@))`
`0 = v^(2) + 2 (g sin 45^(@) - mu g cos 45^(@)) (d)/(2)`
`= (g sin 45^(@)) d + (g sin 45^(@) - mu g cos 45^(@))d`
`0 = 1 + (1 - mu) rArr mu = 2`