Question

An object is thrown vertically from a height of `9 m` at `4 m/s`. How long will it take for the object to hit the ground?

Answer 1

`t approx 0.9 s`

Explanation:

Assuming no air resistance and using the equation
`s= ut + 1/2 g t^2`
Substituting given values and of `g = 9.8 m / s^2`
`9= 4t + 1/2 9.8 t^2`
Rearranging
`1/2 9.8 t^2 +4t -9 =0`

`implies` `4.9 t^2 +4t -9 =0`

Solving the quadratic equation using the formula
`t=(-b+-sqrt (b^2-4ac))/(2a)`

`t=(-4+-sqrt (4^2-4 times 4.9 times (-9)))/(2 times 4.9)`

and ignoring the `- ve` value of t

`t=(-4+13.28)/(9.8)`