1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Dropping a package with initial velocity

  1. Jan 27, 2015 #1
    1. The problem statement, all variables and given/known data
    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: v0 for the package equals the speed of the helicopter.]

    2. Relevant equations
    1) vf2 = v02 + 2aΔx
    2) vf = v0 + at
    3) xf = x0 + v0t + ½(a)t2
    4) Quadratic Formula

    3. The attempt at a solution
    Using the third equation with Δx = xf - x0 = -100, v0 = 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 v0 with 5.3, a with -9.81 and Δx with -100. This leads to vf2 = 5.32 + 2(-9.8)(-100). vf = -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?

  2. jcsd
  3. Jan 27, 2015 #2


    User Avatar
    Homework Helper

    [itex]\frac{44.58+5.3}{9.8}=5.09[/itex] seconds
  4. Jan 27, 2015 #3
    Thank you so much! I see: I subtracted incorrectly
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted