1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    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!

Potential energy of an object with initial velocity.

  1. Oct 11, 2009 #1
    1. The problem statement, all variables and given/known data
    A .300-kg ball is thrown vertically upward with an initial speed of 10.0 m/s. If the initial potential energy is taken as zero, find the ball's kinetic, potential, and mechanical energy at it's initial position.

    2. Relevant equations
    1/2mv(f)^2 + mgy(f) = 1/2 mv(i)^2 + mgy(i)

    3. The attempt at a solution

    I understand how to solve the problem. From my equation I've plugged in the 10 m/s for the inital and zero for the potential. Is potential energy zero because the book said it was? What I don't understand is why potential energy is zero when initial velocity is 10 m/s. If there is initial velocity shouldn't there be a numerical quality in the y direction? To be more clear, if an object is initially moving at a certain rate, shouldn't the ball have left the person's hand and given the ball some sort of height even a little bit?
  2. jcsd
  3. Oct 11, 2009 #2


    User Avatar
    Homework Helper

    PE = mgy = 0 when y = 0 and the thing is, you can define y to be zero wherever you like. Sea level? Ground level? In this case, the height where it leaves the hand and when t = 0.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook