A stone is dropped from rest and takes 0.4 s to cross a window 8 m high. Taking g = 10 m s⁻², the distance of the upper edge of the window below the release point is:
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A stone is dropped from rest and takes 0.4 s to cross a window 8 m high. Taking g = 10 m s⁻², the distance of the upper edge of the window below the release point is:

G1 Physics · Accepted Answer

Let v be speed at the upper edge. For crossing the 8 m window in 0.4 s: 8 = 0.4v + 5(0.4)² = 0.4v + 0.8. Thus v = 18 m s⁻¹. From release to upper edge, v² = 2gh, so h = 18²/20 = 16.2 m.