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: Mechanical Energy - Two Questions

  1. Oct 20, 2005 #1
    The questions read...

    1.) An Olympic runner leaps over a hurdle. If the runner's initial vertical speed is 2.2 m/s, how much will the runner's center of mass be raised during the jump?

    2.) A pendulum bob is released from some initial height such that the speed of the bob at the bottom of the swing is 1.9 m/s. What is the initial height of the bob?

    What are the formulas I would use? I only want the formulas for now becuase I would like to try and solve it myself. Thanks!!!
  2. jcsd
  3. Oct 20, 2005 #2


    User Avatar
    Homework Helper

    Well, I won't give you the formulas, but I'll give you a hint or two.

    On the first one, the problem is the same as if you asked "what height would an object reach if it's initial speed were 2.2 m/s vertically upward?". The fact that they're asking about the runner's COM makes no difference.

    For number 2, think about it from energy considerations - at the bottom of its arc, the pendulum bob has a certain amount of kinetic energy. Where did that energy come from?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook