# Free fall

How long does the stone fall freely into a depth of 80m? What speed will it hit the bottom of the abyss?

Result

t =  4 s
v =  40 m/s

#### Solution:

$s=\dfrac{ 1 }{ 2 } g t^2 \ \\ g=10 \ \text{m/s}^2 \ \\ s=80 \ \text{m} \ \\ t=\sqrt{ \dfrac{ 2 \cdot \ s }{ g } }=\sqrt{ \dfrac{ 2 \cdot \ 80 }{ 10 } }=4 \ \text{s}$
$v=g \cdot \ t=10 \cdot \ 4=40 \ \text{m/s}$

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