Correct Answer - C
Resultant of `N` and `N (= sqrt2 N)` is equal to `mg cos theta`
` :. sqrt2 N = mg cos theta`
`:. N = (mg cos theta)/(sqrt2)`
Now kinetic friction will act from two sides
`:. a= (mg cos theta - 2 mu_(k) N)/(m)`
Subtituting the value of `N`, we get
`a = g (sin theta - sqrt2 mu_(k) cos theta)`