A stone is dropped from the 25th storey of a multi-storeyed building and reaches the ground in 5s. In the first second, it passes through how many storeys of the building? (g=10m/s2).
A
1
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B
2
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C
3
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D
None of these
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Solution
The correct option is A1 Suppose h be the height of each storey By using second equation of motion, we know that s=ut+12at2 As the stone is at rest initially ⇒u=0 Then, 25h=0+12×10×t2 =12×10×52 ⇒h=5m In first second, let the stone passes through n storeys. So, n×5=12×10(1)2 ⇒n=1