Case-I

In order to fall, h₁ = ut + 0.5 at²

h₁ = 0 x t + 0.5 gt²            ...(i)

Case-II,

In order to throw up,

h₁ = ut - 0.5 at²

h₁ = 25 x t + 0.5 gt²                            …(ii)

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from eq(i) and (ii)

h1 + h2 = 25t

100 = 25t

t = 100/25

t = 4s

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Therefore the two stones will meet after 4s.

∴ Putting t = 4s in equation (i)

h₁ = 0 x 4 + 0.5x 9.8 x 4 x 4         

h₁ = 0 + 78.4

h₁ = 78.4 m

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Therefore both the stone will meet at 78.4m from the top or (100 – 78.4) = 21.6 m from the bottom.