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: Kinetic Energy and Velocity

  1. Dec 26, 2009 #1
    1. The problem statement, all variables and given/known data

    A ball at the top of its drop has 15 J of potential energy, neglecting air resistance, what is the kinetic energy at the bottom of the drop? What is the velocity?

    2. Relevant equations



    3. The attempt at a solution
    Because the problem is asking for the kinetic energy and velocity at the bottom of the drop, I guessed that both the kinetic energy and velocity would be 0.
     
  2. jcsd
  3. Dec 26, 2009 #2
    Energy is conserved. So you must have 15 J of energy at every position during the drop.
    What is the equation for kinetic energy? And were you given mass the mass of the ball?
     
  4. Dec 26, 2009 #3
    The equation for kinetic energy is KE=(1/2)(m)(v2). I was not given the mass of the ball.
     
  5. Dec 26, 2009 #4
    Unless I am missing something then you need that... the mass of the ball.

    Unless you were given the height from which the ball was dropped (presumably from rest)?

    You could have a larger mass dropped from small height, or a smaller mass dropped from a higher position, both of which could yeild 15 J of mechanical energy... But would give you diff. answers if you wanted to find v from kinetic energy.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook