A machine, which is 72 percent efficient, uses 36 joules of energy in lifting up 1kg mass through a certain distance. The mass is the allowed to fall through that distance. The velocity at the end of its fall is
(A) 6.6 ms–1
(B) 7.2 ms–1
(C) 8.1 ms–1
(D) 9.2 ms–1
