First slide

Rectilinear Motion

Question

A stone is dropped from the 25th storey of a multistoried building and it reaches the ground in 5 s. In the first second, it passes through how many storeys of the building? $(g = 10 {ms}^{- 2})$

Moderate

A

1
B

2
C

3
D

none of these

Solution

Suppose h be the height of each storey. Then
$25 h = 0 + \frac{1}{2} \times 10 \times t^{2} = \frac{1}{2} \times 10 \times 5^{2} or h = 5 m$
In first second, let the stone passes through n storey. So
$n \times 5 = \frac{1}{2} \times 10 \times (1)^{2} or n = 1$

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