A 0 . 4 kg mass takes 8 s to reach ground when dropped from a certain height P above surface of earth. The loss of potential energy in the last second of fall is ______ J . [Take g = 10 m s - 2 ]

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Displacement in n th second is given by S n = u + a 2 2 n - 1 Here, displacement is 8 th second is S 8 = 0 + 1 2 × 10 × ( 2 × 8 - 1 ) ⇒ S 8 = 75 m Loss of potential energy is Δ U = m g S 8 = 0 . 4 × 10 × 75 ⇒ Δ U = 300 J .

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