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December 18, 2014

December 18, 2014

Posted by **Rose** on Sunday, October 24, 2010 at 10:18pm.

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 -
**Quidditch**, Sunday, October 24, 2010 at 10:25pmHow are you solving it? What answer are you getting?

- Physics -
**Rose**, Sunday, October 24, 2010 at 11:03pmWell 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 -
**Quidditch**, Sunday, October 24, 2010 at 11:19pmYou 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.

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