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A stone is dropped from the top of a building. When it crosses a point 5 m below the top, another stone starts to fall from a point 25 m below the top. Both stones reach the bottom of building simultaneously. The height of the building is
Explanation
Height of the building = $h + 25$ For stone- 1, $20 + h = 10t + \frac{1}{2}gt^{2}$ And for stone-2, $h = \frac{1}{2}gt^{2}$ Putting value of h from eq. (ii) in eq. (i) $20 + \frac{1}{2}gt^{2} = 10t + \frac{1}{2}gt^{2} \therefore t = 2s$ Therefore, $h = \frac{1}{2}gt^{2} = \frac{1}{2} \times 10 \times 2^{2} = 20 m$