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: Free Fall Questions

  1. Oct 7, 2008 #1
    1. The problem statement, all variables and given/known data

    45. A freely falling object requires 1.50 s to travel the last 30.0 m before it hits the ground. From what height above the ground did it fall?

    2. Relevant equations

    x = xi + Vit + (1/2)at2
    Vf2 = Vi2 + 2ad

    3. The attempt at a solution

    First found the initial velocity from 30.0 m left
    30m = 0m + Vi (1.5 sec) + (1/2) (-9.81 m/s2) (1.5 sec)2
    Vi= 27.36 m/s at 30 m away from ground

    Distance from original height to 30 m left
    (27.36 m/s)2 = (0 m/s)2 + 2 (-9.8a m/s2) d
    -38.15 m = d

    total distance = 68.15 m

    I hope this is right! Thank you!
  2. jcsd
  3. Oct 7, 2008 #2


    User Avatar
    Homework Helper

    You have the wrong sign for the Vi in the highlighted equation, and the distances should be swapped, but you got the right result.

    Otherwise, looks good to me anyway.
  4. Oct 7, 2008 #3
    Yes, I posted this because I was unsure about the signs of the two distances. That makes much more sense.

    Thank you very much!
  5. Oct 8, 2008 #4


    User Avatar
    Homework Helper

    I don't believe this is right.The left hand side should be -30m since the displacement is downward.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook