- #1

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## Homework Statement

A helicopter is ascending vertically with a speed of 5.30m/s . At a height of 100m 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

_{0}for the package equals the speed of the helicopter.]

## Homework Equations

1) v

_{f}

^{2}= v

_{0}

^{2}+ 2aΔx

2) v

_{f}= v

_{0}+ at

3) x

_{f}= x

_{0}+ v

_{0}t + ½(a)t

^{2}

4) Quadratic Formula

## The Attempt at a Solution

Using the third equation with Δx = x

_{f}- x

_{0}= -100, v

_{0}= 5.3 m/s and acceleration = -9.81, and the quadratic formula, I get the right answer of t = 5.09 seconds. However, I don't get why this other logical method does not work. Using equation one, I substitute v

_{0}with 5.3, a with -9.81 and Δx with -100. This leads to v

_{f}

^{2}= 5.3

^{2}+ 2(-9.8)(-100). v

_{f}= -44.598 m/s. Plugging this value into the second equation I get -44.58 = 5.3 - 9.8t. t equals 4.09 seconds. What did I do wrong?