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: What speed will the ball hit the ground?

  1. Apr 17, 2012 #1
    A ball has a mass of 240g. (which would be 0.24kg?) is moving through the air at 20.0m/s with a gravitational potential energy of 70J. With what speed will the ball hit the ground.


    Ek=mv^2/2 (kinetic energy)
    Eg=mgh (Gravitational potential energy)
    Ek=mgxdisplacement (if you don't have velocity?)

    I would appreciate ANY help...I don't get what I'm supposed to do.

    P.S. the answer in the book says it should be 31.4m/s :)
  2. jcsd
  3. Apr 17, 2012 #2
    You assume that the groud is zero potential: Then the initian kinetic energy is [itex]T_i =1/2mv_i^2[/itex]
    And the initial potential energy is 70J the 70J is all being converted to kinetic energy when it falls so make your equation and solve it:
    [itex] E_{initial}= 70J+T_i = E_{final}[/itex]
  4. Apr 18, 2012 #3
    Thank you :)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook