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: Energy ratio?

  1. Oct 14, 2008 #1
    What is the energy ratio (Ef/Ei) of a system on Earth that has a final velocity of 3901.5 cm/s, initial velocity of 249.9 m/s, and a height of 0.006 km.


    E = K + U
    = 1/2mv^2 + mgh

    Ef = 1/2mvf^2 + mghf
    Ei = 1/2mvi^2 + mghi


    It appears that the object is being forced upwards since the vi>vf. I tried several times setting hi = 0 and hf = 6m, but I can't seem to come up with the correct answer.
     
  2. jcsd
  3. Oct 14, 2008 #2
    You do want the energy ratio... did you find Ef and Ei and then divide? Also -- I notice here that vf seems to have units of cm/s... is that right and did you take that into account?... might just be these bookkeeping things.
     
  4. Oct 14, 2008 #3
    Yes, I'm trying to solve the energy ratio. I did take into account that vf has units of cm/s. Under normal circumstances, hf = 0, and vf>vi. I made the assumption, based on the values given, that hi = 0, and that an upward force is being applied.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook