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: 2 balls dropped from a building

  1. Nov 5, 2007 #1
    1. The problem statement, all variables and given/known data
    A ball is thrown straight up from the edge of the roof of a building. A second ball is dropped from the roof a time of 1.00s later. You may ignore air resistance.
    If the height of the building is 21.0m, what must the initial speed be of the first ball if both are to hit the ground at the same time?

    2. Relevant equations
    2s=ut+1/2 at^2

    3. The attempt at a solution

    For the second ball,
    ....v comes out to be 20.298m. Then i found t to be 2.069s. Assuming the first ball was in the air 1 second longer, its time is 3.069.

    However, I' not sure how to proceed with the equations for the first ball, since I don't know the maximum height reached by it, though v is 0 at this point.
  2. jcsd
  3. Nov 5, 2007 #2
    since you know the time, acceleration, initial and final positions, you should be able to use x = x_0 + v_0 t + (1/2) a t^2 to find the answer.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook