Using the information given, it's not possible to answer that question.
Regarding the cinder block, however . . .
Potential energy = (mass) x (gravity) x (height)
8 joules = (mass) x (9.8 m/s²) x (6 m)
Mass = (8 J) / (9.8 m/s² x 6 m) = 0.136 kg .
(A real cinderblock has about 67 times that much mass.)
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We have no information that would enable us
to answer the question about the apple.