Question

a stone dropped from the roof building takes 4 seconds to reach the ground. find the hieght of the building

Answer 1

Task. A stone dropped from the roof building takes 4 seconds to reach the ground. Find the height of the building.

Solution. A stone moved with initial zero velocity and constant acceleration $g=9.8\ m/s^{2}$ due to gravitation. Therefore the distance which it pasees by time $t$ is given by the formula:

$d(t)=\frac{gt^{2}}{2}.$

For $t=4$ this distance is equal to the height $h$ of the building, so

$h=d(4\ s)=\frac{9.8*4^{2}}{2}=\frac{9.8*16}{2}=9.8*8=78.4\ m.$

Answer. $78.4\ m.$