# 1D Motion homework

A helicopter is ascending vertically with a speed of 4.00 m/s. At a height of 125 m above the Earth, a package is dropped from a window. How much time does it take for the package to reach the ground? [Hint: The package's initial speed equals the helicopter's.]

So using the displacement formula $x=x_0 + v_0t + (1/2)at^2$, I did $-4.9t^2 - 4t + 125 =0$ at first, because the package was travelling downwards and so its initial velocity would be negative. However, instead, solving $-4.9t^2 +​4t + 125 =0$ returned the correct answer (I just fit in the equation using the hint). But I don't understand why then the initial velocity of the falling package would be $4.00m/s$, not a negative value.

• Isn't the package initially moving upward relative to the ground? – Bill N Sep 8 '17 at 21:27

There's a typo, the equation you want to solve is $-4.9t^2+4t+125=0$.