# Physics

posted by .

For some reason I keep getting this problem wrong. Please Help!

A helicopter is ascending vertically with a speed of 9.00 m/s. At a height of 90 m above the Earth, a package is dropped from a window. How much time does it take for the package to reach the ground?

• Physics -

How are you solving it? What answer are you getting?

• Physics -

Well I saw on a related problem someone wrote:
Package height Y at drop time t is
Y = 120 + 5 t - 4.9 t^2

Set Y = 0 and solve.

but I have no idea what that means...

• Physics -

You are headed in the right direction.
That is a distance formula when there is uniform acceleration which is gravity in this problem. The formula is:

s2 = s1 + vt + (1/2)(a)t^2
where:
s2 = final distance
s1 = initial distance
v = initial velocity
a = acceleration
t = total time

Your initial distance above the ground is 90m. The initial velocity will be the vertical velocity of the helicopter when the package is dropped. The final distance will be 0 as you said. Plug all the numbers into the equation and solve for t. Remember that the acceleration will be negative here.