Helicopter dropping a package
I am having trouble determining the signs (+ or  ) for acceleration and velocity. Here is the question:
A helicopter is ascending vertically with a speed of 5.10 m/s. At a height of 105 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: v(initial) for the package equals the speed of the helicopter.]
I know I have to use the following equation to solve the problem: y = y(initial) + v(initial)t + 1/2(a)(t^2).
I have determined that y(initial) is +105 m, y = 0. Because the package is falling downwards, I will make the velocity 5.10 m/s. Because the package is picking up speed right before it hits the ground, the sign of acceleration should be the same as the sign of velocity. Thus, a = 9.8 m/s/s. However, when I plug my answers into the equation, I do not get the right answer. Can someone explain to me what is wrong with my logic?
