[" A block of mass "m" is placed on a surface with a vertical "],[" cross section given by "=(x^(3))/(6)" .If the coefficient of friction "],[" is "0.5," the maximum height above the ground at which the "],[" block can be placed without slipping is: "],[[" (a) "(1)/(6)m," (b) "(2)/(3)m," (c) "(1)/(3)m," (d) "(1)/(2)m]]