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: 2 Quck Questions on Work and Energy

  1. Jan 8, 2009 #1
    1. The problem statement, all variables and given/known data

    1. If a 0.2 kg ball is dropped from a height of 8 m, what is its kinetic energy when it hits the ground?

    2. Jane, looking for Tarzan, is running at top speed (4.6 m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she swing upward?

    2. Relevant equations
    Kinetic Energy = (1/2) mass*gravity*height
    Potential Energy= mass*gravity*height
    not sure if this equation is right.... distance=(1/2)(gravity)(time^2)
    Velocity= (change in distance)/time

    3. The attempt at a solution
    my work got deleted for both the question (error in webassign) and now I have no idea how I got the answers. (both wrong) But they were 9.5J for the first one and 14.2m for the second question.
  2. jcsd
  3. Jan 8, 2009 #2


    User Avatar

    Staff: Mentor

    Your KE equation is wrong. It's mixed up with the correct PE equation. Fix the KE equation, and you should get the correct answers.
  4. Jan 8, 2009 #3
    woops I had it actually I just wrote typed it out wrong it is (1/2)mv^2
  5. Jan 8, 2009 #4
    For part a, maybe im missing something, but did you say that your answer of 9.5J was correct? because im thinking otherwise unless im missing something very obvious.

    E(i)=E(f) ---> PE=KE in this case correct?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook