Question

A boy drop a stone from a cliff , reaches the ground in 8 seconds calculate (1)final velocity of the stone (2) height of the cliff [take g =9.8 m/s square ??

Answer 1

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Answer 2

Given:

Initial velocity (u) = 0

Time (t) = 8 seconds

a = g = 9.8 m/s

To find:

(1) Final velocity of the stone = ?

(2) Height of the cliff = ?

Formula to be used:

$\[v=u+at\]$

$\[S=ut+\frac{1}{2}a{{t}^{2}}\]$

Calculation:

(1) Final velocity of the stone

Let the final velocity of the stone be 'v'

$\[v=u+at\]$

$\[v=0+(9.8)\times (8)\]$

$\[v=78.4m{{s}^{-1}}\]$

(2) Height of the cliff

Let 'S' be the height of the cliff

$\[S=ut+\frac{1}{2}a{{t}^{2}}\]$

$\[h=ut+\frac{1}{2}a{{t}^{2}}\]$

$\[h=0\times (8)+\frac{1}{2}\times (9.8)\times {{(8)}^{2}}\]$

$\[h=0+4.9\times 64\]$

$\[h=313.6m\]$

Final answer:

(1) Final velocity of the stone = $\[78.4m{{s}^{-1}}\]$

(2) Height of the cliff = $\[313.6m\]$