Correct Answer - a
`mu_(s) = tan 30^(@) =(1)/(sqrt3) = 0.6`
`mg sin 30^(@) - f_(k) = ma`
`R = mg cos 30^(@)`
`f_(k) = mu_(k) R = mu_(k) mg cos 30^(@)`
`:. Mg sin 30^(@) - mu_(k) g cos 30^(@) = (g)/(2) - mu_(k)g (sqrt3)/(2)`....(i)
`s = ut + (1)/(2) at^(2)`
`4 = 0 + (1)/(2) a (4)^(2)`
`rArr a = (1)/(2)`
a का मान समी (i) में रखने पर
`(1)/(2) = (g)/(2) - mu_(k)g (sqrt3)/(2)`
`mu_(k) = (g - 1)/(g sqrt3) = (9)/(10 sqrt3) = 0.5`