Question

A stone is thrown straight drownward wirh initial speed of 4.8 m/s from a height of 51 m. What is the times it takes to reach the ground ?

Answer 1

Here we go to use the basic equation of kinematic of a movement with the acceleration of the gravity

In our case the initial point is     and the initial velocity (the sign minus is because the stone is thrown downward). The final height is , so the time that takes to reach it

Here we have a second grade equation, and the solution is given by

Here we have two solution. Like one of them is negative the solution of our problem is the other