58. An elevator starts from rest and accelerates upward with constant acceleration a = 2g. A small ball is released from rest relative to the elevator at a height h above the floor. The ball then falls and strikes the floor. What is the speed of the ball just before it hits the floor, as measured in the ground frame?
(A)
(B)
(C)
(D)
(E)

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統計： A(0), B(1), C(2), D(0), E(0) #3847834