A 0.4 kg mass takes 8s to reach ground when dropped from a certain… | JEE Main 2023 (29 Jan, Shift 1)

Q17JEE Main 2023 · 29 JAN · SHIFT 1Medium

Conservation of Energy

A 0.4 kg mass takes 8s 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 ${}^{2}$ )

Numerical answer type. Work it out, then open the answer.

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Answer: 300

Distance fallen in the $n$ th second from rest: $s_n = \frac{g}{2}(2n - 1)$ .
$s_8 = 5 \times 15 = 75\text{ m}$
Loss of PE $= mgs_8 = 0.4 \times 10 \times 75$
$= 300\text{ J}$

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